Where are you getting $4m?
Regardless what VW wanted, what we know is that the Pats did not want to pay VW $4.5 roster bonus. That could mean that they could not afford him/$8m cap/not renego now or did not think his projected performance in 2015 was worth bringing back at a $4.5m minimum. Perhaps VW and team saw...
34 year old DT Darnell Dockett signed a 2yr/7m deal w/ SF and his 1st year comp is $4m.
28 year old Ricky Jean Francois signed 3/$9m w/ $4m in guarantees/cash value in 2015.
Since those players are not as good as VW, we assume VW's contract will be > $4m in 2015. There are 10 FA DTs ranked higher than VW that could possibly get more.
According to
http://walterfootball.com/freeagents2015DT.php there are 10 players ranked higher than VW. I agree with a handful of them being better than VW. Their asking price could drop after the FA period rush, the draft and once OTAs and TC start.
You also have 5 DTs in the draft that are projected to go in the top 37 picks that would be potentially less than $4m.