Okay, first thing, to all those crying censorship, get the hell over it. MSN does not have the capacity to limit your free speech on the Internet. It can regulate your behavior on the internet- if you're foolish enough to use their service. But what MSN does with it's chat rooms is hardly enough to worry about censorship.
This doesn't mean I agree with the supposed reason. There is only one thing that can protect and defend your children against the boogeymen of the Internet- you. See also: sex and violence on television, drugs, media culture, etc. I get offended when companies try and sway the public by having "child protection" tools. My parents didn't use them for me, and you know what? I broke the rules. Chatted with strangers, snuck looks at porn and then purged the history. All that crap. However, I was raised not to be so foolish as to hand out personal information. I dunno, from a young age, I was intellgent enough to police myself without too much trouble. I'd hope my kids end up the same way.
As for how much safer this is:
Requests can only be made if users know the other's e-mail address, says MSN, which means most children only have "buddies" who they know outside the internet.
Do you know how many teenieboppers have websites? Hell, my sister has one with AOL. And these kids put their email on. And most of these kids don't use discretion in adding buddies (as I note with my sister's 150+ buddy list).