The popularity the Playstation brand has managed to maintain has really helped for Europe plus the fact that Japanese are hard to convince to go for the 360.
The negative press, false media and exaggeration of everything that went wrong with the PS3 should have really killed the console.
On top of that it seems that Sony also has some dynamic contingency plan and patience with the product. The reduction of costs of the hardware according to some reports is large. I had concerns before the PS3 was released that it would end up like the saturn because lets face it:
They took almost every mistake SEGA did with the Saturn and put it in the PS3. The only difference is that Sony does react according to the behavior of the market, instead of sitting there doing nothing, expecting that the competitors will fail and the market will work on their favor.
The PS3 doesnt do bad in US but it sure has a large gap from the 360.
I expect that once games such as GT, FF and MGS appear the PS3 could surpass in yearly sales the 360 for 2008. The 360 has had a tremendous build of games in 2007, most of the big titles were released then. The list of anticipated games is smaller currently (it is remained to be seen what MS has in store at this years GDC). I am expecting Sony to reduce the worldwide gap but it is questionable whether it will surpass the total 360 sales because of its strong presence in the US.
I think that it is an advantage that MS won the US market since it is a more uniform market. The European market is fragmented, and the Japanese market is small, which makes harder to predict how much the PS3 can do in software sales, or how the consumer behaves.