My MacBook is not an Apple. It is a LEMON

On what basis does Apple determine which repairs they will cover on Macs that are within the 1 year warranty? A month ago, Apple covered the replacement of my MacBook's "topcase" because some cracks had developed on the edge of the gray plastic panel surrounding the keyboard. They said that this was a common problem among the MacBooks. Yesterday, the gray plastic panel surrounding the LCD screen began to crack in the same manner. This part is made from the same kind of plastic, so I figured that they could fix it. Well, today, at the new W14th street store, no luck. The kid at the Genius bar very politely explained that SINCE THIS PART IS NOT CURRENTLY UNDER RECALL, IT IS NOT COVERED UNDER THE WARRANTY. Furthermore, the kid said that he'd never seen this problem on other MacBooks. Interestingly, he also said that if they see enough people coming in with the same problem, maybe they'd change their mind. That's a load of bull$#!+, don't you think? SO, my question is... Does a part have to be under recall in order for it to be repaired under warranty? Does it have to be a predetermined issue before they will acknowledge that this is a workmanship problem? I'd like to think that the nice kid made a mistake, or that there was some sort of miscommunication. But this experience left me pretty p!$$ed off at the way they handled my situation. PS: The last time I had gone to the Genius Bar, the guy tried to sell me that preferred customer thing. He smiled like a used car salesman and explained that with the preferred customer status, my computer would be fixed ahead of everyone else's. When I declined, he said that he'd do everything he could to handle my repair quickly anyways, but the next time, I might not be so lucky. I had to wipe all the slime off my computer when he was done with it. What do you think is going on here?