You don't know what you're talking about, which is why it's funny that you tried to say everyone else doesn't understand the Pats offense. Jennings could play in the slot as well as many other players. I'm not calling Welker an overrated bum like some have around here, but there are plenty of players that could play that position. The reason they wouldn't is because it'd be a waste of their talent to limit them in that way.
The reason Welker is perfect is because he lacks the talent of these other players... his talent is reached in this role and he plays it to the best of his ability, and gets all the props in the world for that. But that doesn't make him a top 5 WR in the NFL or anywhere close to it.
Lets say you have a 6'9 WR who comes in only when the team is in the red zone. Lets say this guy catches 15 tds on a season but finishes with something like 35 total catches. We'd say he's very valuable and may even be worthy of a pro bowl but nobody would argue that he's a top 5 or even 10 WR in the league. This is Welker... but he doesn't even put the points on the board that my hypothetical WR would.
The games that Welker missed, Edelman put up almost the same numbers. The role inflates his stats. He's important. He's good. He's far from great.