The Jimmy Johnson trade chart is not really useful anymore because now you have the rookie pay scale. So say you are at 7 and you think you could get the same guy you want at 10, the 7th pick gets a contract worth $24,099,130 (total for 4 years) whereas the 10th pick gets a contract of $20,141,444 and the 15th pick gets a contract for $15,586,376. So you save $9 million in actual money to move down from 7 to 15. granted you are not getting the same player at 15 as you would at 7, but you have to consider is he worth $9 more than the guy at 10?
Many times, especially now with the rookie wage scale, teams want to move back, because they know their guy can be had lower so why not move back and save the money, but they can't find a trading partner.
Lets look at last year, in the first round the following tackles were drafted:
#5 Giants, Andrew Thomas $32,345,588
#10 Cleveland Jedric Willis $19,702,914
#11 Jetes Mekhi Becton $18,446,048
#13 Buc Triston Wirfs $16,288,026
#29 Titans Isiah WIlson (already cut) $11,568,389 Tits had to pay him over $6 million for 2 snaps!
But you can see the other 4 tackles are easily interchangeable and some would say you could even go backwards in draft order to gauage their effectiveness in their rookie years. (Wirfs, Becton being higher than Thomas Willis). But the Bucs are paying Wirfs HALF of what the Giants are paying Thomas over their first 4 years.
The bottomline is, if a team doesn't really see a difference in who they are going to take, then moving down is really in the teams best interest, so don't expect a kings ransom, last year the Bucs traded pick 117 to move up one spot from 14 to 13 (they also go a 7th rd pick in return too).
The Pats traded down 13 spots into the second round and only picked up a late third round pick for it.
The rookie pay scale makes these top ten picks very hard to trade, because no one wants the salary that goes with them.