That's funny. Who else charges third-party developers for the privilege of creating plugins for their DAW? (I can think of only one other example: Native Instruments collecting fees for libraries that run under the free Kontakt player. But at least you get a free player.) TransVST would have potentially cut Avid out from that source of revenue.
Ever wonder why the Pro Tools versions of plugins are so much more expensive than the generic native versions?
EDIT: a related link:
http://www.protoolerblog.com/2012/12/07/the-real-reason-transvst-got-pulled/