Yeah, after taking another look, I think you're right. Looks like we're more or less locked in to that spot for the foreseeable future.
I had to take a look back to see who I was forgetting because in my lifetime at least, Illinois has never been a consistent producer of high caliber pros. I think this explains it:
Illinois players have made 17 NBA All Star appearances. Deron Williams made 3. The other 14 happened before 1968.