The may have omitted USB 3 due to the interference that it can generate in the 2.4GHz range.Why doesn't the new AirPort Extreme have USB 3.0! I'll just sit back almost forever with my N's until they put USB 3 in them Geez!
Thunderbolt would've been too expensive to add. If your current base has N capability and is working fine, you have no reason to replace it. I went from a 9.5 year old Airport Extreme 802.11b/g to the current one with 802.11ac. I should've replaced it a while ago, but it still works and I'm keeping it as a spare.You'd think it would have USB 3 and/or Thunderbolt on it. It makes no sense to me. I'm sticking with my 2nd generation AEBS still. Since the new one is AC and my new iPhone 5s and iPad Mini w/Retina display only have wireless N. That also makes no sense. Why didn't they put AC in these new products too?