Sony & Att&t is pushing the 3g model thats why they announced the 3g bundle, of course it will outsell the wifi intially, but after the initial release of the Vita and the bundles dry up since its only first shipments only, wifi will outsell 3g by 3:1, so no developers will make a feature in a game require 3g, because that would alienate a majority of the Vita owners. Im sure you will see a couple of intial games do small features like Disgaea, that is a added bonus but really no big deal at all.
The biggest downfall of Vita 3g is Sony partner with ATT&T....plus you cant even play multiplayer over 3g signal, only Wifi. Im sure most of us have cell phones with internet connection, so we can accomplish everything the 3g model can as far as browsing, social networking. If you must have 3g, why not root your cell phone to a mobile wifi hotspot and connect Vita to that, its free and takes 15 mins to root a phone at most.