If you are with a provider that is everywhere anyway, like Vodafone or T-mobile, the idea of roaming is very obviously just about gouging money. It's not as if T-mobile has to pay a third party by the Mb to ship data from Germany to the UK, they own all the infrastructure anyway!
I think this is an important point, which is freqently forgotten. So many apps that would be useful in a foreign country are useless because they require internet access. When I went to Bulgaria last year I would have loved to have a translator app for my iphone, but every single one available required internet access, which there's no way I'm paying for at £3/MB!