Nice catch, that's a huge step forward. But is that not on the nexus 7?
"Available only on tablets.", see http://www.android.com/whatsnew/
I think there's a certain sense that a phone is a much more "personal" device than a tablet. While it would probably be possible to add multi-user support, it would be more difficult, and be less useful, than on a tablet.
"Why Android Jelly Bean 4.2′s Multiple User Account Switching Is Tablet-Only? (Hint: Nokia Patented It For Phones)"
http://techcrunch.com/2012/10/29/why-android-jelly-bean-4-2s...