I believe that this, like the thermal grease issue, is a serious case of poor assembly. When I first received my MBP it refused to eject a particular DVD. I initially managed to solve the issue by holding the machine upside-down and pressing the eject key but decided to investigate further.
I powered down, inserted a disc half way and then viewed the laqptop from the side. The portion of the disc that protruded from the machine had a slight downward slope and, when viewed from the front, one side was higher than the other. It seemed obvious that the slot in the drive was slightly out of alignment with the slot in the case. I then removed the top panel, took the drive out and slightly loosened the screws holding the mounting bracket on the side that appeared high. This allowed the bracket to be moved up and down by about 0.5 mm. I then held the bracket in its highest position and gently re-tightened the screws.
Upon reassembly, I tested with a half-inserted disc again and now it was level when viewed from both front and side. I reckon that some discs are slightly thicker than others and so can hit a portion of the case upon ejection.
As an experienced engineer, I have no qualms about tweaking the assembly of my computers but I shouldn't have to and most owners certainly won't want to!
IMHO, this, like the thermal paste situation, is another issue that Apple needs to address on their assembly line, maybe with a jig to locate brackets more accurately on the drive. It definitely shouldn't be left to individual owners risking their warranties in order to get their machines running acceptably.
G5LC, G4 1.4 GHz cube, 2.0 GHz MBP, 15 1.67 GHz & 1 GHz PBs, 800 MHz PB Mac OS X (10.4)