A number of NBA players have contributed financially and in other ways to their alma maters.
I don't think it's an obligation by any means, and JC's comments may have been a means of deflecting any pressure any alumni been feeling. If there's chatter on message boards that they should contribute, there may be chatter in the players' ears as well. This way, JC has made it clear it's not their responsibility, and if any of them give anyway, it makes them look that much better.
One thing I will say is that JC did not build his program on a foundation of super-duper-star high school players. He's had, what, nine McDs AAs? It's not like he's brought in a ton of kids who every single top program was pursuing and who necessarily would have been successful anywhere. So from that perspective, the argument could be made that JC/UConn have developed basketball players more than some of the other top MBB programs out there.