There's no fragmentation, and no Steam sign-in. Valve games are played with PSN IDs on PSN servers, being able to link one's PSN account to a Valve account in order to redeem a PC copy is a feature, not fragmentation.
The problem with PSN is that it was and has been a complete afterthought for Sony in relation to PS3 and is just an extension of the existing infrastructure that existed for PS2. Microsoft thought everything out with the OG Xbox and then implemented it properly, from the start with 360 and now we are seeing the benefits of that forwards thinking. Sony have learned their lesson though and Vita is much more sensible with social integration and I expect PS4 to launch with XBL feature parity and some added extras.
I find it highly amusing that a company embroiled in a fight with EA because they refuse to "open their network" is complimenting another company for doing it.
You can use common USB and Bluetooth devices for gaming, as long as the developers want to. e.g., Keyboard and mouse is also confirmed for Counter-Strike: GO.
You can also stream or download assorted movies and TVs from quite a few providers now. Just link your PSN account with theirs.