I see fault on both sides, but in this case as the hotel promised the upgrade it should have been honored:

OP: I think a case of unreasonable expectations. Platinum benefits only accrue to one room. Unless you are using SNA's it is not a benefit of Platinum to get upgraded to suites in advance. (I recognize it happens but it is not a benefit of being Plat.) Additionally, the suite has to be available for the entire stay at check-in. Finally, the upgrades are only to "select-standard" suites, and the hotel decides which category is select-standard.

There is also an internal upgrade priority, which (IMO) I find perfectly reasonable. I get it that all Plats are not equal, and I'm worth more to a hotel I spend half my annual stays at vs. one I've never stayed at before.

Hotel: All of the above said, once the hotel staff promised to upgrade you, they should have followed through. Period.