Well, I have never seen a WR run a 5.0 40, so the 40 time shows some threshold of a player's ability. If Chris Johnson runs a 4.6 instead of a 4.24, he doesn't get drafted and certainly doesn't run for 2000 yards in an NFL season. No, a 40 times doesn't matter by itself, but it shows a player's potential capabilities and how that can translate on to the football field. So who gives a crap about 40 times? Every NFL coach, scout, GM, owners, people who evaluate players for a living - exactly what we are doing here, evaluating a player.
Thats comparing apples to oranges. I do believe a 40 time is more important when evaluating a RB(Chris Johnson) who can touch it 25 times a game versus a WR that may be lucky to touch it 6-10 times a game. I prefer if the WR has good hands, has good balls skills when its up in the air, routes, coming out of their breaks, and so on. The 40 yard speed is the least of my worries, and personally I think its overrated! Besides I think he has developed a little later than most and with a year or two in the S&C program that 40 time will come down anyway...