It's funny that I was in a lively back and forth about the topic until I asked how many minutes the Brit I was talking to got for free when he was in France, Germany, Latvia, Greece and Russia. Oddly I didn't get a reply to that, it's like he forgot entirely about the thread!
Not a Brit, but I pay 21 euro/mo for 100min/1GB/unlimited text (don't need more and don't want to pay for what I don't use), and it doesn't matter where I use them in the EU and a few of other countries in the world. No roaming charges or other extra charges for phone or data usage in those countries. At least not for 60 days out of the year. At the same time I get data speeds higher than some people have at home everywhere I go, and the concept of dropped calls is something alien to me.
For the record (Re: Tinmania's remark), while the European Union is about half the size of the US, Europe actually covers a significantly larger area than the US. Regardless of your definition, you will find excellent GSM coverage everywhere, even in remote and low populated areas.
That said, having a gazillion different networks and companies using the same network standards makes it a lot easier because the cost is more spread out. Having 3 networks that are also incompatible with each other makes creating a network with 100% coverage for such a large area a very very expensive ordeal for the companies in question.