WDWRC is a CM with the Reservations Center, or at least based on previous postings.
As to knowing for a fact, I don't think even the agents know for sure 100%, but I would think WDWRC is making a very educated guess based on his/her knowledge of the system and how it works and I would have to agree.
If bookings are already secured in large number for the summer months, there truly is no reason to offer any discounts.
As to previous summers, bookings were not that high months prior to the summer dates. They filled up more last minute and many filled due to discounts.
Of course some of the bookings could be a false read. Meaning that people have book rooms they won't keep unless they get a discount, and that messes it up for everyone including themselves.
Only time will truly tell, but I don't think it looks good at all for June. If hurricanes start popping up and gas prices for travellers start rising, then cancellations might occur which might have Disney offering some last minute discounts for July and August.