I'm actually surprised HTC and Verizon hasn't completely forgotten about this handset yet! On a side note, my Thunderbolt started doing an update the other day and I thought that it was for ICS already. As it turns out, it just rebooted the phone after a 65MB update, went to the bootloader and wasn't able to reboot until I pulled the battery a couple of times. Way to go Verizon.
Why is this Verizon's fault? It would actually be more HTCs issue than anything. Plus I don't know if you read up on a lot of forums or not but HTC released the new ICS update sheet saying the ThunderBolt will receive ICS late July early August. The update you received was just to hold you over until the ICS update starts.