The features isn't the problem, hell, I could single-handedly write software in 6 months that offers all the same features. Features aren't the difficult part.
Polish is one exceedingly difficult part, the system has to be usable by the most computer-illiterate people out there. Microsoft have a department whose sole job is to research and test usability - its one of their biggest. Second is the integration, this is the biggest issue of all. Have you noticed how ALL the Xbox 360 games use Live (even if its a little in the case of Kong) seamlessly? How you login once, and that same login is used for all games, and you don't need to re-login when you start a new game? All the games allow the Xbox guide to open on the left pane, allowing for the user to compare their stats with other people at any time. This in itself is major for two reasons: 1 the game doesn't go mental over losing full control over the console and 2. two different applications are accessing the video card at the same time. This sounds an awful lot like Vista's 3D scheduler.
Sony will no doubt meet the features sooner or later, but they won't meet the reliability, or the integration. Anyone whose played a SOE MMO game, knows that the account management is barely centralised across all their MMOs, its a complete mess of different designs, different systems, all trying to meet common ground. Worse still is the servers running the MMOs are rebooted daily (I remember in EQ2 when they said that after the initial month or so there won't be daily restarts), and the servers can be down for extended periods of time.
Chances are that behind the scenes, Live is far, far more advanced than you actually see. A lot of features will be present, but just not utilised. It wall also be very expandable, and anyone in the software bizz knows that quickly developed (and/or designed) applications are very difficult to expand upon.
. Don't like P2P systems like live 
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