Not sure I agree 100%, but in terms of logic he's got a point.
The only game that even came close to beating out MGS4 for the sheer amount of GOTY's in '08 was GTAIV...
And lets be honest here; all of the additions to the game weren't even all that, the cover system was especially wonky and the world didn't really feel all that alive-you had barely any measure of communication with the inhabitants.
I'm saying this as an owner of the game. RDR just looks so much better; the cover system looks functional, the online play is integrated into the game world, the ecosystem and frequent wanted posters plastered all over the world, etc. All these additions make it feel like what GTAIV was trying to be.
Personally, my Game of The Year so far is Mass Effect 2, with Alan Wake following closely behind as an honorable mention, but if critics loved GTAIV for the flawed experience that it was, why wouldn't they love RDR???