Excellent point indeed! In providing IPv6 services to consumers, building the transport infrastructure is not the most challenging thing. There are two other major gating factors: 1)Getting the user device updated to support IPv6, 2) availability of service resources. Environments where these two factors are easy to manage will have an easier time rolling out IPv6 services.
Along with the 3G "endorsement" of IPv6, mobile providers are in the category mentioned above. The mobile handsets have a short refresh cycle which means the user devices can be updated very quickly (not to mention the fact that all mobil OS today support IPv6). Mobile providers are, to a certain extent walled in gardens so they are in a good position to manage most resources neccesary for their service offering.
Long story short, 3G together with the specifics of mobile provider environments provide a very good environment for IPv6 (early) adoption.