There are a number of real reasons. The other two consoles aren't bad. They are both good offering different experiences that you don't get with a PS3. But every year it becomes more clear that the PS3 has the most staying power.
The first party lineup is way better. Blu-ray built in is nice for game developers and for consumers who want to watch HD Movies.
I just see Sony taking more risks like LittleBigPlanet and Heavy Rain.
I don't really think there is any denying on a technical level that the console has more potential. But when it comes down to it only first party games and exclusive games will ever showcase what it can do, as no developer making multiplatform games wants 1 version to look way better than the other version.
Bottom line each has their own market with some overlap. But what makes Sony stand out is the first party games not really the system itself.