While his size is a part of the issue, you're failing to see the TYPE of player he is. Douby is a shoot-first guard. That's the role he played at Rutgers, which is NOT what the Kings need him to be.
I wouldn't go attacking the other posts, though because of wackiness. SAR has been a starter before...a pretty decent one actually. Garcia is maturing as a player, and it wouldn't surprise me if he were to eventually start. Salmons did OK as a starter.
BTW, there are plenty of tall and lacky [sic] wide receivers in the NFL. It all depends on the system for which they're drafted, which I think is the crux of the argument. Unfortunately, Douby's the square peg in the round hole.