It was a game that was hurt by it's predecessor despite it being a fantastic game, add in the upcoming heap of releases, the games released over the last few months and the whole heap of releases that PS3 users also could have picked up during the year and Resistance 3's sales are perfectly understandable.
2011 is the year of the 'drop out', meaning that due to a packed release schedule, some games are forced to fold. Crysis 2, Bulletstorm and Resistance 3 are all 'drop outs', they were all critically acclaimed, original in their own way and they all came from well respected and known developers and publishers, but they couldn't take the punches of a busy year.
I also believe that a shooter fatigue is setting in, big games will be out of reach (as seen with Gears, Battlefield, COD) mainly due to their brand names and marketing budgets, but anything below spectacular or a 50 million dollar marketing budget is going to get less than stellar sales numbers. Some games will be exceptions though, RAGE and Uncharted 3 will succeed because they are different enough, but I honestly think that the last successful mid tier (market status wise) military based FPS will be Killzone 3 and that's mostly because it released so early in the year.
When Cliffy B said that B-Tier (once again, by brand status in the market and not game quality) games are going to or are struggling, I think that his mainly referring to B-Tier shooters, because as we've seen with games like LA Noire, Catherine, Dark Souls, Deus Ex and Dead Island, success can be found on the busy release season battlefield.