Apple treats a dirty lens as a malfunction to be repaired by Apple if still under warranty.
True but even a new computer can experience a dirty dvd lens from lint, dust, etc. If you have applecare, and the time to ship it back, and to wait 7-10 days for repairs and retuning shipping (assuming one takes the the time and effort to ship it back to apple as opposed to driving to an authorized apple repair center) apple then has the option to replace it with a new unit, or simply open it up, troubleshoot, give it a shot of compressed air, seal the unit, test it again, and ship it right back to you.
A quality dvd lens cleaner kit from Maxell or 3M often comes in handy. I own 6 separate macs (and not all of them are currently under applecare).
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