Here in the States, it's treated as a character flaw and research pales in comparison.
As someone who's lived in both countries - though fortunately had a body type that wasn't seen to be overweight in either country (technically I am overweight right now, but nobody I know thinks so) - I can honestly say I question this. In the UK, I routinely witnessed overweight people mocked and verbally abused. In the US, there's at least a general recognition that losing weight isn't easy, and gaining it is. Which is not to say that there are no assholes in the US either.
I'd always assumed it was due to the environment. The UK is generally urban, which means people get plenty of exercise, and spend 20 minutes getting to and from work leaving more time in their day for healthy food preparation. In the US, which is more suburban, a combination of barriers to walking (some, like bizarre zoning, legally enforced) means people have to seek out exercise, do not get it naturally, and the 30-45 minute each way commute leaves even less time for food preparation, leading to widespread consumption of relatively unhealthy premade meals.
That leads to a situation where people in the UK weigh far less than the average American, which means there's less empathy - fewer people in your circle are likely to be overweight, so you're allowed to make more negative judgments AND the fact that so few people are overweight makes you more likely to treat them as doing something "wrong", as obviously they're "doing something" that the vast majority of people aren't (which, ironically, is less likely to be true in an environment with fewer overweight people - you're more likely to find people in that environment who do the same things as you, but have biological/genetic/medical/etc reasons for gaining weight.)
Is there better research in Europe? No idea - if there is, it probably has to do with a willingness of governments to fund research that has no agenda beyond better health, while I'm willing to bet most American research into obesity has an end goal of selling more Nutrasystems and Slimfasts. (That said, I'd love to be proven wrong on this.)