A factor may be that some Europeans are looking ahead towards the future, a PS3 version provides no worries of RRoD and disc scratching. The more 360 games you buy the harder it becomes switching to another platform.
When our 360 died, we weighed the pros and cons. The main factor for not selling the 360 was that we did invest quite a bit in the platform, premium + extra controller + memory card + ~6 games and would sell it at a good loss. But we decided going PS3 + Wii only was the best option for our family.