They may be buying stuff on PSN. I have ony bought 4 retail games at launch and the rest was digital.
Yeah the tough thing with the Vita is that unless Sony decides to share some digital sales numbers with us (yeah, right!) there is always going to be a larger margin of error between Vita game sales numbers and it's closest competitor, the 3DS. I'm not saying it's going to be a huge margin by any means but it's a margin that definitely exists, especially among the most hardcore software buying crowd like us early adopters.