I'm Plat, have stayed at the Park Lane 2 times & was upgraded to a suite the 2nd time. The first time no upgrades were available to Plats because the Olympic choosing committee who was deciding between London & some other venue got all the suites.
However, in that instance I was upgraded to a huge room with plenty of space.
But as everyone knows, the longer the stay the less chance of a suite upgrade. Not many hotels are willing to take a suite that they can sell out of circulation for 7 days. Also, there are times a hotel may have suites available some of the nights but not all of them so technically the suite isn't available for a stay. Not all hotels want to deal w/ musical room changes (my term) - ie, reg room one night, suite for a few nights, then back to reg room.
Re: the accessible room. Depending on how booked the hotel was that may have been what was available at the time & if your parents didn't have status, they drew the short straw. Also, not all ADA rooms are 'gross'. In some instances they're the same as other rooms with a few mods.
Cheers.