Why? It never mattered if Moss caught a ball or not. Unless a guy had "Revis" on the back of his jersey, Moss demanded a minimum of 1 1/2 defenders on every down. I also think that Wallace is a much better route runner than you give him credit for. He's not the best in the world, but he's probably above average and getting better.
I guess the wild card in this is Brandon Lloyd, and if Belichick and McDaniels feel that 1) he's close enough to Wallace in ability and 2) they can sign him, that it's not worth ponying up the first for Wallace.
I think they would rather have a guy like Lloyd or Wayne who can run the deep ball but also will run the intermediate routes. Steve Smith of Carolina if he had a better attitude is another.
It wouldn't be out of the question for Bill to trade out of 27 or 31 as usual. Franchise Welker and then trade him for a second. Sign both Lloyd and Wayne to deals that together aren't that much more than Welker would be getting with the franchise tag.
Trading out of the first round for second and future first, great value check.
Trading a 31 year old receiver that you got 5 pro bowl seasons out of for a second rounds which was more or less what you paid 5 year ago, great value check.
Not giving up a first for an RFA and having to pay him 2X either of the guys you picked up, great value check.
Wayne, Lloyd, first rounder 2012, second rounder 2012, first rounder 2013 vs Welker, Wallace and first rounder 2012.
Less money, less risk and as diversified of an offense. Edelman and the TEs make up for Welker's production and Wayne and Lloyd give you solid outside depth that open things up for the guys underneath.
I'm not saying it will happen. I'm just making the case it's more likely than Bill giving up a first and paying Wallace a ton of coin when he's more or less a deep threat only.
I know people will jump on this and to be honest I want Welker back at hopefully less than the 9.6M/year of the franchise tag but if that went down the same people barking about Welker being too important would celebrate Bill's genius.
EDIT: BTW I was one of the people who wanted Wallace really badly coming out. When they took Tate my jaw was on the floor and when the Steelers took him with the next pick I was pissed for days. I've been wrong about tons of picks too so the point isn't about being right it's just that I do like Wallace but in retrospect perhaps he landed in the right spot.