I don't get it.  If the PS3 is more popular in Europe and Japan, and the PS3 is of equal numbers to the Xbox 360, why do Xbox 360 versions of games sell so much better than PS3 versions?

This is not always the case, so I must point out the contradiction in your argument.

Maybe faulty tracking here? Or the Xbox has a broader western audience (the audience that buys the most games)

This is not the case for all games.

Call of Duty =/= all games.

The western market.  Been going on for years.

Software Sold

X360 - 776.53

PS3 - 687.3

This is even without Japan and most japanese games so yes, X360 sales more the majority of the time.

not all games. RE, FF sell better on PS3. but to answer your question i think its cause the 360 usually has the better multiplats

Not the case for all games look at FIFA, MK, AssCreed III.
Also the Japan market and US market are two completely different demographics.

There are plenty of games that sell better on PS3 than 360

Batman Arkham series

Assassin's Creed series

Fifa series

Resident Evil

Etc.

It's because of the lead the 360 has in the US market. But in Europe even Call of Duty sells more on PS3.

Maybe because of PS Plus and maybe not every ps3 owner buys ALL the main stream games.
For example: american people buy a lof of shooters right? European people a bit less, in some genres american sales (country with more 360s sold than ps3s) have great impact worldwide in my opinion. I think ps3 players have more different tastes among them. (sorry if there are some grammar mistakes)