Thanks to everyone for the advice. It certainly seems that the rules are not as I thought. My understanding was that if a room was available at check in you would be offered an upgrade. Originally suites weren't included but these were added to the list a few years ago.

At issue seems to be the meaning of the sentence "All upgrades are granted on a space-available basis, as determined at the time of check-in." What I was told at check-in is that this property holds the suites and offers them to Platinums upon payment of an additional nightly fee.

I never ask for an upgrade when traveling alone but in this case I'm with the wife and two teenage boy's and the space would be nice. We had booked a "family room" at additional cost even though it is just a standard room with two beds because this property like most European hotels doesn't allow 4 persons per room the way you can in the US.