What's the difference between oblige and obligate? Speculating, is the latter an Americanism of the British former? Or is there any distinction about what/who has caused someone to be oblig(at)ed to do something?
Neither is more correct than the other. They're both common words. In fact, they're sometimes different words. For instance, to oblige someone is to do something for them that they want you to do. "She asked me to pick up dinner, and I obliged her by getting some lasagna from a little Italian place down the street."
That's not the same as obligating someone, which means to make them HAVE to do something (or feel that they have to). "Although the statue was meant as a birthday gift, he obviously felt obligated to get me something expensive in return, despite my protestations."
There is a dialect aspect to it as well. What's wrong with "obligate"? In US English nothing is wrong with it. In Australian English everything is wrong with it. Here's how I'd have put it.
"Although the statue was meant as a birthday gift, he obviously felt obliged to get me something expensive in return, despite my protest."
In my dialect "oblige" is fairly common but "obligate" is never heard. The distinction that Uriel mentions is not made in Australian English. We use "oblige" for both meanings.