I'm not saying Moss has been perfect, he has had a couple of bad drops and the 3 fumbles do suck, but you can't honestly say that is reason enough to not have him MVP.
Yes, Welker is very important at moving the chains, but so is Moss. As I have highlighted, Moss actually has a higher percentage of first downs, 66.5% of his receptions are for first downs, 16% higher than Welker.
Also, if it was so easy for a 6-4 receiver to catch lob passes for TD, you would see more guys with 10+, 15+ TDs a year... you don't. He is a scoring machine because he is practically uncoverable. How many times have we seen him getting doubled in the endzone, the pass is just lobbed up, and Randy jumps over the defenders and snatches the ball from in front of them...
The point is that Moss has just 10 fewer first downs than Welker, while having a much higher percentage compared to receptions. He is less than 150 yards shy of Welker in yards and Moss is the one who is scoring.
The other thing is, who is the biggest threat to score whenever he catches the ball...
Now I love Welker and I DO agree that he is an important part of our offense, but simply saying that without him we wouldn't get to the endzone is just ridiculous. You can say that (correctly) about every team in the NFL. You can't just have one WR out there, they all need to contribute. The point is, though, that Moss is the most dangerous and most important WR out there.
Also consider this. Why, if Welker is the most dangerous WR on the team, would teams STILL focus on shutting down Moss with double/triple coverage all game while allowing Welker to be in 1-on-1 or zone coverage and getting 7 receptions a game? I'll give you the answer. It's because teams realize that if it is Moss that is getting 7+ receptions a game, they have no chance.
Some more stats for you:
Welker has averaged 2.2 first downs per game in his career, Moss 3.5 per game.
Welker has averaged 44 rec yards per game in his career, Moss 78.
Welker has averaged 0.15 TD per game, Moss 0.80.
The numbers don't lie. Moss has just 10 fewer first downs than Welker, just 150 less yards, but more than 4 yard per receptions and an incredibly important 8 more TDs than Welker. Oh yeah, and he has the job of facing the best CB and double/triple coverage all game while Welker gets his 1-on-1 (often with linebackers) or zone.