Agree to a certain extent, but there are numerous examples of Top-3 picks getting traded to somewhere in the Top 10 and the team that originally owned the Top-3 pick being very happy with the trade (best example that I can think of is the NYG trade-up for Manning with San Diego, as that produced for SD Rivers, Merriman (as a 1st rounder in the next year) and Kaeding... 3 Pro-Bowl quality players))
Teams that typically pick in the Top-5 have a dearth of elite talent at all positions, so they normally would be reluctant to pass up their best chance of grabbing an elite talent in favor of more but lower probability chances of grabbing very good or elite talent lower in the draft. However the Pats, if they are drafting Top-5 with the Oakland pick in 2011 would not be the typical team that drafts Top-5, so their option space is much wider, in my opinion.
Let's extend the original scenario, the Pats have #3, and their top 2 players are gone (Peterson and Jones for example), then their value board has an elite WR, a 3-4 DE, a RB and a LT all ranked very closely to each other. Any of those four players would be a massive talent and value upgrade for the Pats at their respective positions. There is also a pair of elite QB, and an elite 4-3 DE on the board that just won't fit the Pats plans. Those three are very good prospects who the Pats rank as legit Top-10 talents and the Pats believe every other Top-15 drafting team also rank as legit Top-5 or Top 10 talents. The Pats are pretty damn sure that one of the QBs will go at #5 to the Panthers
So as the Pats go on the clock, they are roughly indifferent four elite players (flip a coin a couple of times and the Pats would be thrilled). The Lions call from #8, they want to move up to grab the 4-3 DE and they offer #8 and the 2012 1st rounder....Now the Pats would still be guaranteed to get one of their guys @ #8 at a lower salary and have another 1st rounder in 2012...
That is the type of scenario where I could easily see the Pats trading down from a Top-5 pick and rolling some of the value into the future year.
Now if the Pats' #1 player is available with the Oakland pick, or there is a clear and significant differentiation between the available prospects' grades, the trade-down option becomes way less likely. But if there is a good value cluster, I can easily see the trade-down.