Its actually up to 35% discount and isn't available on all the hotels all of the time. You are right as well that often its cheaper to book a package with tickets included than room only with AP as any special offers aren't applicable to room only.
Most people with AP either stay off site - the partner hotels are quite nice and reasonably priced or you can book a room for one adult (and any free children on offers) then add the 2nd or extra persons at check in and they will pay only room tax for the night (usually literally a few euros per night) - the extra people get breakfast/access to EMH etc same as if they had booked a package. Pop over to DLP board if you want more info on this as its done quite regularly by people there
Are you staying off site this trip?