Well, let's be clear on what the rules are for retired players. A retired player only counts against the salary cap in two situations:
1) He signed a multi-year deal when he was over 35; or
2) There are "cap recapture penalties" because the player's contract was front-loaded.
So if a team signs Johnny Veteran, aged 34, to a seven-year deal that pays him the same amount per year every year, and he retires before the end of that contract, there is no salary cap hit post-retirement.
The exceptions exist to deal with the problem of cap circumvention. Teams would sign players to long-term deals containing "fake" years -- seasons that everybody knew, and in some cases had a wink-wink unwritten agreement, would never be used, the purpose of which was to stretch out the salary and reduce a cap hit. And teams would front-load a deal. So you sign Johnny Veteran to a seven-year deal that pays him $10M, $10M, $10M, $2M, $1M, $1M, $1M, when Johnny really only expects to play for those three $10M seasons. Effectively you're paying him $10M a season for three years, but the cap hit is $35M / 7 = $5M per year for those three years, and then drops off when he retires. (I'm exaggerating the numbers for effect -- I don't think the CBA ever permitted this big a disparity.) But of course you could rarely prove that there was collusion and that the team and player didn't intend for the contract to be fully performed, so it was a headache for the league to deal with circumvention -- the Devils eventually got slapped for going too far. Hence the recapture rules -- they effectively told teams that, if you want to front-load long-term deals, go ahead, but you're taking a risk of getting nailed down the road if the player retires early. The Predators chose to take that risk (as, for that matter, did the Flyers in making the offer sheet).
The CBA has subsequently narrowed the extent to which contracts can be front-loaded, so this tends to be less of an issue now. Weber is just an anomaly because he signed a massively front-loaded deal (a huge signing bonus contained in a Philadelphia offer sheet designed to make it hard for Nashville to match) that wouldn't even be allowed today.
So this really isn't a situation that is likely to recur. Luongo is retired, and Parise and Suter just got bought out. Which, by the way, is another reason why I suspect that the news articles are making a lot of fuss over nothing -- the NHL is not likely to kick up a big fuss about Weber being put on LTIR. He seems legitimately injured, so factually Nashville would have a strong case to make, and I doubt the league is interested in picking a dumb fight with a southern U.S. franchise just to enforce a rule that is not terribly relevant any more.
Jim