I'm in my third consecutive year as Platinum, and even though Delta claims that K fares are only "marginally higher than L in most markets", the routes I usually fly make K fares over $200 more than L. This really bites; you can't offer a perk, then take it away and expect not to alienate some of your passengers who have demonstrated extreme loyalty, many times going out of their way, schedule-wise, to fly Delta. I suggested that they restrict L upgrades to Silver/Gold, and still allow Platinums (the ones who've shown the most loyalty) to upgrade. Or as TWA did, stop being tightwads and spend money to increase the number of first class seats.
Should I be penalized for planning in advance (and getting an L fare) by not being allowed to upgrade? What's going to happen in a lot of places is that frequent flyers will wait until the last minute to book flights, thereby almost ensuring that L fares will be sold out, and ultimately costing their employer more money. The result of that is that the *employers* will start to specify that employees travel something other than Delta to save money. Vicious circle.
By the way, most other major (domestic) carriers, fully aware of the ire of Delta's frequent flyers with this, are MORE THAN WILLING to match Delta's PREVIOUS frequent flyer rules if you fly on their airlne.