Dicha know?
A Compact disk has data packed into it in less denser conditions than a DVD. You probably know that data is written onto cd's into a spiral track pattern. A DVD simply has increased number of these spiral tracks. If you get an audio cd and drill a hole through it, chances are the cd will work fine. Even more, A cd uses a larger pit size onto where data is recorded, these are the little bumps where data is recorded. Hence it is easier to rectify these pits than the smaller dvd pits. So its not just that its a dvd writer or a reader. Now, a dvd writer basically uses 2 lasers. But it not physically 2. When it reads a disk, it uses the normal reading laser power and when writing, it uses the high power laser. A dvd writer never uses a "more powerful laser" when it dosent need to! So it comes down to one thing. Its your DVD drive, one might be better than the other, one might have better features that allow it to read cd's better, features from the manufacturer. Clean dvd's using a cleaner disk, remember the softer the disk the better. Or just to be in perfect peace of mind, open your drive up and using a delicate brush, some alcoholic cleanign fluid and a lot of skill, clean the drive yourself, oil the motors a bit and oil the laser assembly.