Based on a survey conducted by the trade group Tiga, there are nearly twice as many developers in the UK that focus on making PSN titles compared to XBLA titles.
The survey covered 100 studios in the UK and 30 of them are creating games for the PlayStation Network where as only 16 of them are making games for the Xbox Live Arcade. This may have something to do with the rumour about Microsoft being over-controlling with what content they put on XBLA. It could also be based on the fact that there are about 5 Sony Worldwide Studios in the UK whereas there's only about 2 Microsoft studios.
These scores, however, are nothing compared to PC and mobile focused games which hold a vast majority over consoles; 41% for PC and 67% for iPhones.