Yeah of course it's going to hold up, some people just can't get a clue when it comes to these contracts. If you wanted to put a positive spin on them, they're sort of an unofficial franchise contract. The teams get some immediate benefit with the lower cap hit, but they assume a long term risk (see: Rick DiPietro). Effectively it's a minor form of cap circumvention, but a line is drawn where reasonable doubt can be made. If a player plays for the full length of his contract whether with the original team or another then everything balances out and there is zero cap circumvention, that only happens when a player retires before the contract is done.
So as long as a team signs a player up to an age where even if unlikely he could still be playing, there isn't really anything the league can do about it. For the dozen or so players on these contracts, you'd have to think at least 1 or 2 will still be playing right till the better end, meaning the league would have been completely unjustified if they voided them.
So the GM's have a good thing going to skirt around the cap with a few players, and this is where the Devils broke. A goalie could play a few more years than a skater (Roloson for example), but there's no way Kovalchuk will be going till he's 45. If the league didn't put a stop to this, it would've been an open invitation for the next team to push that limit even further. So an upper age limit is established, where it can reasonably be believed that the player could still be playing. Ootherwise before you know it teams will be trying to sign a guy till he's 60.