It's all about service popularity (fame)
I agree that Tango.me is the no.1 choice when it comes to Anroid video chat but let's not forget the no.2 competitor in this area which is a recent startup called ooVoo.com - yahoo messenger also supports video chat using a dedicated plugin. So yes - sad but true - Skype's video support is late and very limited. Fring and NimBuzz were already mentioned in a different comment.
Biting the hand that feeds IT
