The Pats also have a brilliant understanding of how to use free agency, especially with short term deals á la Moss, Revis, Browner, etc. Something Ted Thompson is rather allergic too.
In fact, the Pats superior utilization of free agency to supplement the draft is what separates them from the Packers in terms of overall success in the last 10 years. I can't help but feel the Packers would have at least played in another Super Bowl in the last few years if they had been a little shrewder with regards to free agent opportunities.
I do agree that TT could do better when it comes to using free-agency (or trades) to his advantage.
This being said, the reason why Pats have resorted so heavily to free agents - Revis aside, virtually all of them on the cheap - is namely because they keep taking risks in the draft and are not as careful with their draft capital as the packers or the Ravens are, for example.
When you miss as much as the pats do on your draft picks - just look at the stats and you will be amazed how many picks, not just late-round ones but 2nd-3rd round too, have gone to waste - this creates holes on the roster, holes that have to be filled with free agents. Even the cheapest of free agents, however, are significantly more "expensive" in terms of cap-room hit than majority of players on a rookie contract.
This ends up hurting the team in the long run, caproom-wise, preventing it from being able to keep some of its own, high-prized free agents or attract others from outside. Pats get away with Belichick's ability to coach up average players to play well beyond their natural ability within the system.
Also, most of these free agents that the Pats have to sign to fill the holes on their roster, are signed to cheap, short-term 1-2 year deals. If their play matches those cheap deals, then you haven't gotten all that much from them as a team (except for players, who perform exclusively on special teams as they tend to be cheap anyway).
Should those players outperform their cheap, short-term deal, however, they are gone within a year as the Pats will no longer be able/willing to afford them. This leads to too quick a turnaround of the roster, which creates lack of continuity and hurts the performance of the team from one year onto the next.
At the opposite end of the spectrum, building thru the draft and getting contribution from most of your picks, ensures (especially after the 2011 CBA) that you have players, grown into your own system, at your disposal for 4 years on cheap rookie deals. This leads to greater continuity and stability of the roster and improves its performance in time.
A potential drawback in the Packers' approach is that you could trust in your draft picks a bit too much, missing out on the possibility to improve your roster thru some free agent signings, here and there, at the expense of some inferior home-grown talent.
This is where I think T. Thompson tends to be a bit too conservative in his roster-building approach and one could argue it somewhat limits how high the Packers could go.
Patriots' approach isn't without its flaws either, though. IMO, had it not been for Brady and Belichick, the Packers approach would have proven superior over a prolonged period of time.