It's not clear to me that need plays a big role in the first pick. Everyone was predicting an edge rusher in the draft for around 5 years before picking up Jones. They had one of the worst secondary's ever in 2011, yet didn't pick up a secondary player with either 1st rounder the next year. After getting Hightower they had two top talents at LBer with Mayo making it one of the stronger positions on the team, yet the next year they grabbed another LBer.
Outside of QB you can pretty much justify any position as one of need, especially when talking 1st round players because they should be an improvement most of the time. I think it just plays a role where your not going to draft a guy if you don't think he can beat out who you have. But part of that depends on how good he is. If he's good enough he should be able to beat out just about anybody.
The counter to those are:
2012: After losing Anderson to FA, getting little out of Ellis and Carter's injury.... as well as only bringing in Scott, DE was a huge need. The secondary was weak, but at least you went in 2012 with a Chung and Dowling (supposedly) healthy and you brought in Gregory. Of course, they still selected Wilson #48 overall.
2013: A cover LB was an enormous need, and had been for a while.
As I wrote above, the lack of an OLB/DE prospect remains puzzling, but just a cursory run through makes it clear that need is a big part of the equation for that first pick.
Seymour - could have gone a lot of ways
Graham - this was predictable, and even more so with the benefit of hindsight
Warren - If polled, I'd wager that at least 80% of Pats fans would have predicted a DT.
Wilfork - A Washington sized hole
Mankins - the one spot without a starter penciled in
Maroney - Dillon fell off a cliff in 2005
Meriweather - Rodney was tailing off, getting injured the past two seasons and Geno wasn't the same
Mayo - Finally a LB!
Chung - Needed a SS
McCourty - the one time a top overall pick appeared to come at a position of strength (Bodden/Butler).
Solder - Light was a question mark and only one more year at most, and LT a premium position
Jones - discussed above
Collins - discussed above
Easley - A pass rushing DT? I'm game!
Excluding Seymour, because the team was a mess, I predicted the position of the player selected first simply by analyzing roster construction 7 of the 13 times. Granted, I had long before decided Bill just wasn't going to select a DE/OLB in the first round, so that may have inflated my numbers a little (though it is also the reason I got 2012 wrong ). It also could be pointed out that the times the consensus top need was bypassed, it was quickly filled and even doubled up (2010 TE, 2013 WR).
It's really illuminating when viewed all at once. Just look at that Warren/Wilfork/Mankins run, I bet even Mel Kiper Jr got those positions right in most of his mocks!