There's a few things we can read into here.
First, the Seahawks had an opportunity to get a player they've been aware of since last year. They made a move, but typically they have a reason at this time of year. The move to get Burley last year was similar, but they grabbed Burley to fill a need for depth at the Nickle spot. Simon doesn't translate well there.
I'd also speculate that Jeremy Lane goes on IR. All we've heard in the offseason is that he's dealing with set backs and trying to get caught up. I'm willing to bet the coaching and medical staff know where he's at right now and they are probably guessing Lane won't make it back.
Simon has flashed potential, but the only thing he's really been able to show is an inability to stay on the field. You can't count on this kid to stay healthy. I don't know if he's snake bit, or just doesn't put the work in physically (very likely as that was a big knock against him at LSU). There was a reason he was available in the 5th round, and it was lack of work ethic and willingness to get prepared. It still seems like that's a problem; every time I've seen him on the field, he looks suprised he's there and unprepared for who he is facing. Just because the Seahawks drafted him doesn't mean that he'll get over his flaws.
They're not liking the depth. It's possible that they were able to get a player they like, albeit a bit raw, to compete for CB depth. Maybe they don't like the kid they drafted, maybe Burley isn't progressing...I can't speculate on individuals, but I can speculate that maybe the coaching staff isn't seeing what they expect out of someone, and they saw a chance to either challenge him, or add a body that has a chance at making an impact.
Our swing guys, like Shead, need to focus on Safety. Pete's already said this, but Kam and Earl being out is pretty serious and we need our backup safeties to focus on that position and not CB. This isn't very speculative, as Pete's already said it.
Williams. Stay with me here. I think he'll work out fine. He was a pretty good CB for the Ravens, I think he was misused in Philly (and had a worse supporting cast). But it's possible the coaching staff is looking for a replacment for next year, when we can save some money by cutting him. It's amazing that we were able to sign Wilson and Wagner, but they can always look to cut salary. Maybe this kid, along with Tye Smith and Simon are in contention for that starting spot next year (well, I know they are, but adding another guy who could work is the FO's M.O.). Schneider is always thinking 2 steps ahead.