It's probably using some high-level Cocoa network framework, and not kernel-level functionality like netstat does. So my guess is only apps using the same high-level net framework are listed.
Because of the user interface. It's a dumb issue, but Lion changed the way table views work. Getting from 0 to MVP was about twice as fast with the new Lion features.
It's something I consider improving, though. Fundamentally, the same app should work on 10.6 too.
