Pres. Obama's speech in Westminster Hall contained the soaring rhetoric one would have expected, and reading the text one can imagine it in delivery and even be moved at one or two points. There were at least a couple of things that jumped out: in one passage he equates "free enterprise" with "the market" (wrongly, I think); and the Roosevelt-Churchill chord is struck perhaps a bit too loudly at the end (don't Obama's speechwriters know about Churchill's view of the Empire? If Churchill had had his way, the British army, which Obama's grandfather, as the Pres. remarked, served as a cook in Kenya, would still be in Kenya). Still, it's hard to avoid Churchill-FDR in this context, and his speechwriters did manage to find a reasonably appropriate Churchill quotation -- something about 'the chirping bird of freedom' -- to end with.
The stuff about the U.S. and U.K. still being indispensable for leadership in the world etc. etc. is entirely predictable; what else could he say? This is not totally wrong, but even if it were he would still have had to say it. You can't get up in Westminster Hall and say "our power and influence are declining, let's decline gracefully, thank you very much." Well, I suppose you could, but you'd have to have really skilled speechwriters to make it go down.