I would like to add: OBLIGATORADE. Obey your thirst.

Wait; that's Sprite. D'oh!

I am mid-investigation. So, while I have not yet found a definitive answer, I can say this much:

There is strong evidence showing that "obligated" is NOT an "Americanism". Consider these references in classic English literature (source: http://www.thefreedictionary.com/obligated ):

- Charles Dickens in 'Great Expectations':
"So, he'd come with a most tremenjous crowd and make such a row at the doors of the houses where we was, that they used to be obligated to have no more to do with us and to give us up to him."

- Jane Austen in 'Persuasion':
"I believe Mrs Charles is not quite pleased with my not inviting them oftener; but you know it is very bad to have children with one that one is obligated to be checking every moment; "don't do this," and "don't do that;" or that one can only keep in tolerable order by more cake than is good for them."