The odds are fairly great. FYI, many of the CDR's are purchased by individuals who are into collecting live concerts, which as more and more time passes bands allow you to do.
Anyway, these individuals have large collections that they have transfered their collections from cassette, reel to reel, Beta and DAT to CDR. Also, the trading community is expansive and it is not uncommon to regularly trade 25-50 or 100 CD's at a time, read each month.
If you do the math you can see that a trader can log anywhere from 600 to 2000 hour a year on a machine, therefore, quickly using up the life of the laser.
I would suggest that anyone thinking of buying a used deck should really know the person they are buying it from and feel they are being totally honest about how many hours have been burned. That way in the end you won't get burned.