And completely usable from a 360, so not really a distinguisher.
It's there for DLNA support. I remember some features are not complete on 360, but I forgot what (related to how PMS uses M2TS). It doesn't matter whether 360 owners or other DLNA clients can use it, since it's something PS3 owners need and can have for free.
Media Center is not a DLNA server. If you have your Media Center connected to your cable, it essentially allows you to forward your DVR/Cable TV to any TV in the house connected to a console, without paying the cable company any extra money. Fully functional, you can watch live TV, record new programs, and also use it for everything you could use a DLNA server for. Never found much use for it myself, since the DLNA media sharing is good enough for my purposes, but for the folks that have a media center, it's incredibly useful.
I think Sony went the PlayTV/Torne route (No PC needed -- which can be a good or bad thing depending on your needs). Too bad it's not available in US.