Like dbhill says, the thing we tend to forget on this side of the ocean is just how big "T-Mobile" is in Europe. Deutsche Telekom is -huge-.
It's very much in Google's interests to have Android phones on any carrier who'll carry them. HTC is rolling in cash as a result of Android where three years ago, they were barely staying afloat. Android's market share is making a pretty good dent in the US industry given that it's only been available for about a year and I'd expect as app developers get on board, the quality and quantity of available apps will rival the iPhone's within a year or two.
The tricky part, of course, is that Apple has what... 3 SKUs for the iPhone currently available, with an 8GB 3GS rumored to be on the way? iPhone development is technically easier because of the limited hardware support needed, whereas Android suffers from a wide array of different hardware models and a huge discrepancy in which version(s) of the OS are available. It's damn near unconscionable that there are still double digit numbers of Android users stuck on 1.5.
T-Mobile is a fine carrier depending on where you live. I'm in the Twin Cities, MN and their 3G coverage is a little spotty in places, but overall it's quite good. Their customer service is absolutely outstanding - I've had to call all of three times in three years and each time, they've been extremely friendly, helpful and willing to go above and beyond to make sure my questions were answered and issues resolved.