By his own standards. He has thrown as many ints as Henne and more ints than Sanchez. He isn't having a bad year comparable to himself. He is having a bad year comparable to some crappy QBs.
How's that for cherry-picking your stats to fit your conclusion!
Manning leads the league in yards and has a 90+ passer rating. He's thrown 26 touchdowns to go with the "more ints than Sanchez" (who has 16 touchdowns). Sanchez also has nearly twice the number of sacks. For Manning that's not an o-line thing, he is really good about getting rid of the ball.
Saying he is having a bad year comparable to some crappy QBs is borderline insane.