The UK association for writers of romance is the Romantic Novelists' Association whereas the US has the huge Romance Writers of America. The RNA is relatively small, a fact which no doubt has something to do with the fact that romance is much less popular in the UK than it is in the US, with 'adult readers [...] turning away from romance to crime and thrillers'. Included among the 'romance' novels are the works of Catherine Cookson which may be better described as family sagas (with romantic elements). The RNA, as its name suggests, is for novelists whose works are 'romantic': there is no requirement for them to write the happy endings which are essential in 'romance novels' as defined by the RWA. We also don't see many books in the UK with the 'clinch' covers which are so often reviled by readers of romance in the US.
So national differences affect the packaging, genre definitions and reception of romance. But do they also affect the tone of even those books which are romances according to the RWA's definition? Juliet Flesch, author of From Australia With Love, certainly believes that 'Australian women's romance is culturally distinctive; in her chapter "The Beetroot in the Burger" she argues that there is an "egalitarianism, independence of spirit, a sense of fair play and a sense of humour" (p. 251) which can be attributed to a uniquely Australian sensibility'.
Getting back to the football, American football players look particularly 'masculine', with their padding exaggerating the size of their shoulders. This is a contact sport where the players literally clash and run into each other. Soccer players, on the other hand, wear clothing which reveals their bodies but does nothing to enhance them, and while players such as David Beckham may be considered extremely attractive to the opposite sex, he's also appeared in a sarong:
Did the different clothes, hairstyles, jewellery, make him less "masculine"? (99.9% of British men live in fear of being less masculine.)
No, it merely meant that the fashion pack began to join forces with the football followers - and worship him. [BBC article]
So what about American v British romance heroes? I tend to read mostly Mills & Boon historical romances, but I venture outside that sub-genre from time to time, and I've noticed a few trends, though I'll not be completely surprised if some more knowledgeable person comes along and disagrees with me in the comments trail. And before I begin, I'll make it clear that, as with all generalisations, I'm sure there are plenty of exceptions.
In the US romances, American heroes are popular, and they're often military or otherwise able to 'protect' a heroine physically/with a weapon. This applies in contemporaries as much or more so than in historicals where the English Regency period still dominates.
In the UK, Mills & Boon sell nothing which is the equivalent of Harlequin's American Romance line. And I'm open to correction, but in the contemporary romances I've read from M&B the tall, dark, powerful hero tends to be Greek, Italian or Spanish. I haven't found one Mills & Boon contemporary where the hero was a UK policeman or soldier, though I have come across one paramedic working with the Fire Service. The most common British hero I've come across is the doctor, usually found in the Mills & Boon Medical Romance. Interestingly, that's a line which is edited in the UK, although Harlequin in the US does sell some of them. It's maybe relevant that the guidelines for the series state that:
Heroes and heroines are equally matched and equally respected professionals. [...] These romances usually involve both hero and heroine working together in a medical environment. The focus should be a developing, emotionally driven romantic relationship pushed forward by the hero and heroine's involvement with patients and their medical treatment, and their medical colleagues.Although this type of hero's special, he doesn't, I think, attain the status of being 'superior in degree to other men and to his environment, [...] whose actions are marvelous but who is himself identified as a human being', of the type discussed by Northrop Frye (see Eric's post below). The heroine is usually just as good a doctor as he is. So maybe UK romances tend more towards the 'realistic' end of the spectrum of romance. I certainly haven't noticed an outbreak of vampire/paranormal heroes here, and those are surely heading off the top of the scale when it comes to being 'superior in degree to other men and to his environment'. If UK romance readers want to read a romance, written by a UK author and published in the UK, with a hero who is 'superior in degree to other men', who is a Hero (with a capital H) or what might be termed a 'God among Men' (though not literally a god), then they seem to have to turn to historicals or foreign heroes, and I notice that the heroes of historical romances written by UK authors are very often affected by the more realistic trend too.
Now it could just be that American men are, indeed, Gods among Men, but I find that a little difficult to believe, just as I'm unprepared to believe that of the men of other nationalities. I've yet to meet any sheiks, but the Greek, Spanish and Italian men I've met are certainly not the arrogant, somewhat chauvinist males presented in the Mills & Boon's I've read . I am prepared to accept, though, that the way masculinity is constructed in US society differs from that in the UK. It's not that long since you had a Wild West, and you can still legally own guns (in the UK gun ownership is now extremely restricted). In terms of literary/popular culture influences, in the US there's the cowboy of the Westerns, and maybe patriotic feeling in the US contributes to the popularity of heroes who are in the military, the police and the fire services. Maybe the greater acceptance of capitalism in the US leads to more respect for entrepreneurs, and so there are more American heroes who are business tycoons.