You essentially answered your own question within your question, man with the last few lines...
It doesn't really mean anything. Its not an excuse, or a plausable one anyway, and if a game gets lower sales on PS3, so what? There are 8 million more 360s then PS3s, there doesn't NEED to be an excuse. If a game sells better on PS3 then 360, though, THAT should raise a few brows, no the other way around.
GOTY Contestants this year: Dead Space 2, Dark Souls, Tales of Graces f. Everything else can suck it.