I'm pretty sure he was talking about Apple having the opportunity to block competing VoIP solutions (say Google Voice). With Gizmo going to Google you can bet that they will be doing really interesting things with SIP on Android.

Background VoIP support in iPhone OS 4 suggests Apple has no intention of blocking these apps; in fact, it seems that they're encouraging them. And as I understand it, G Voice is not a VoIP solution yet. (And that's not to say I agree with it being blocked. On the contrary, their UI — the supposed rejection reason — doesn't look much different from the other dialer apps, including Skype.)

As far as "competing VoIP solutions", it's not like Apple is competing in the VoIP arena; they seem perfectly content to let other companies battle it out.