British sales oracle GfK-ChartTrack has revealed that Portal 2 is selling best on the Xbox 360, by quite a significant margin. In fact, a mere 35% of boxed Portal 2 copies sold on PS3, compared to the Xbox 360's 54%.
While it's not unusual for the Xbox 360 to get the edge in multiplatform console sales, it's interesting to note that the PS3 version is largely considered superior, coming not only with Steam support, but a free copy of Portal 2 on PC. It's also worth considering that the PS3 is generally a more regarded and desirable console in the UK, so it's odd to see such low comparative figures.
One's first thought is that the notorious PlayStation Network outage -- now in its sixth day -- has had an impact on the sales. It's quite possible that the complete inability to play half of the game has caused consumers to pick up the Xbox 360 version. I dare say more consumers know about the PSN's downtime than Portal 2's PS3 bonuses.
In other news, the PC version netted 10% of boxed sales, but that doesn't include Steam, so who cares?