You also can't measure individual merit by team accomplishments.
As Taint said in the other thread, no fan is saying "Gee, I hope my QB shreds the league this year, leads in TDs and yards, and we miss the playoffs!". I'd take Dilfer over Manning in a heartbeat if it was the difference between my team winning the Superbowl or not.
But when measuring the best invididual player at a position, rings are a mere part of the equation. Hell, Kaepernick would have "won" the Superbowl this year despite not playing in his teams first 10-12 games (can't remember exactly how many it was). I think the 49ers are a great example - same team pretty much the last two years. Changed QBs this year, still got ultimately the same result. Does that mean Smith is equal to Kap? No - it means its a team game.