(Note: this thread was split from the UK board at: http://chowhound.chow.com/topics/799656 -- The Chowhound Team)
I think there is wider issue here though - I don't expect to get roast beef and Yorkshire puddings when I go to France, but it seems that many people from the States expect everything they get there to be available here, and to be of the same quality. So while there may be the odd place that does Buffalo Wings or Mexican food, for example, the availability and quality is not likely to be the same as in the States, where they are almost national dishes.
I can understand expats craving foods from back home, but that is just the way it is - and I am glad that not everything is available here, because the increasingly globalised nature of things is gradually eroding the beauty of national and regional cuisines, and by default, the differences between cultures. The ubiquity of "full English breakfasts" in parts of coastal Spain has really diluted the food culture of those areas.
I might be contradicting myself here, as I do enjoy the fact that there have been many influences from different countries in British cuisine over hundreds of years... The availability (and quality, I guess) of non-indigenous foods in every country is generally dictated by the history of immigration and the settlement of people from other countries - thus Mexican food (as the example i used above) is readily available in the States, but not in the UK.
Sorry if this is a bit long-winded and off-topic, but (while this may not apply to you as someone who lives in London) I think it important that travellers recognise this and enjoy what London does well, rather than seek out what they can get at home, which will either not exist, or will be a disappointment.