I think this can be explained.
Many franchises associated to the PS are not actually owned by Sony. While many did start or get popular on Playstation, most aren't owned by them (FF, KH, MH, DMC, RE, MGS, Tekken, etc etc). It can't be denied that the PS brand had a vast majority of the biggest franchises exclusive to Sony systems, simply because they sold so much.
Now that the tides have turned, people want to play these games on their preferred system. With so many "PS games" going multiplat (or jumping ship altogether), GoW3 somehow gets mixed in there... people are just getting spoiled with the amount of franchises that have turned, and are either greedy, or are ignorant to the fact Sony owns the IP. The latter is actually understandable, a few years ago I couldn't tell you what IP's Sony or Microsoft owns (in fact people still get things mixed up here).
