The NFL took a huge hit last year in ratings. I think (and hope) Thursday night football will eventually come to an end. The NFL is still king and making lots of money, but it is very possible that the cap would actually decrease due to a drop in revenue. If anything I would guess that is more likely then it automatically going up again.
With that said, a percentage of the cap or projected cap is in order and that seems to be lacking in the discussion. It would be bad business to accept that rising prices will always rise (cue 2008 housing crash).
This unpredictable cap reality is why I like the Rams general strategy of paying up front. I prefer super high guaranteed salaries in year one and two over a signing bonus.
As to the QB discussion. Well there are only 32 starting QBs, they play the entire game and touch the ball on every possession. There are not even 32 true starters in the league, it is a very difficult position to fill and it is the biggest single factor regarding championships as a result of a position. A DT does not play every down and sees rotation. There are more then 32 starting quality DTs and it is not a position that seems to be as large of a determining factor in regards to superbowl championships.
I guess I see QBs like tech companies that even though they have not made any money venture capitalists might throw all kinds of money at them. The chance at something huge is there and makes the gamble worth it. A top QB could be worth a lot of money (think beyond championships, think identity and jersey sales etc). A DL is like a traditional company that had the ability to make a ton of money but you do not see as much investment based on speculative potential, instead it is based on actual sales and projections based on increased market share, etc. You cannot compare stock price or investment dollars with a tech company to that a traditional business.
If you sign a QB to a lot of money and he gets injured it is a huge hit but an acceptable gamble. For any other position it is not as acceptable. Is AD worth making an exception for? Yes I believe so, but I also do not think we should use QB contracts in the equation at all. However I do think including other offensive players such as RBs or WRs and LTs is legit and good.
I do think the owners are preparing for some adjustments in general and it appears the safety position is the place they are starting. So many seem to think that huge record setting contract will look like a deal in a couple of years, but I have a feeling we are in a market correction season and it could be the albatross that the Joe Johnson NBA contract was for years. In 2010 he signed a contract making him the highest paid player and was a top three for years to come. In 2011 the new CBA was ratified changing the max salary from a 6 year at 10.5% raise annually to a 5 year at a 7.5% raise annually. If something like that happened in the NFL it could end up looking bad (kind of how the one year jump in NBA revenue led to a lot of crazy and horrible signings: see Luol Deng and Timofy Mozgov). I would like to lock up AD and make him one of the highest paid positional players as he should be, but I would want to protect myself. If his camp insists in an opt out clause I would insist on less guaranteed money and more incentive based pay. If they say no, I would call them out. Either you are betting on your player getting more in a few years based on play or you are not, choose what system you want. Protection based on guaranteed money or max based on performance pay. It has to be one or the other, if they are wanting both it is a non starter.