It doesn't sound like a change. MPC was never able to block seats...all they could do was put a block on "request", and then control would block it day-of. It was (and probably still is) a joke. I always found that - whether or not MPC "requested" it or not - the seat next to me was "blocked" if the flight was, say 50% or less full. Whenever the flight had more people than that (which is precisely when you want the block), it didn't happen. And hence the only way to assure yourself of a seat block is to physically get to the check-in counter early, and have them block the seat for you by calling control.