It always helps when it's free.
The PlayStation Network remains free to access for everyone and the new PlayStation Vita just launched; it's only at 1.2 million sold now, but that number will certainly grow in the near future.
The bottom line is that according to Sony, speaking at GDC and as reported by Develop , there are 90 million confirmed PSN accounts around the world. SCEA Developer Relations Manager Ted Regulski said the numbers were compiled from accounts registered on the PS3, PSP, and the freshly released Vita. He also said Sony was "the only major console publisher to allow self-publishing."
"There are others but they have publishing rules that aren’t much fun, and there are no weird limits you have to hit in order for us to pay you."
Regulski added that the PSN offers a better royalty rate than either Microsoft or Nintendo, which of course is incentive for developers. As for the total number of PSN accounts, there's no doubt that users find ways to have multiple accounts on the same machine, so perhaps we should take "90 million" with a grain of salt. Still, there's no denying just how far the PSN has come in five short years.