I have had a memorable contact with Iomega a few years back on why their drives burn at not the speed that I dictated. If I remember right, they said that it's because of a "special" feature on their drive that prevents coasters. If the drive isn't able to detect the media and it's speed, then it'll burn at 2x or 4x. What does this mean? The drive is crap unless you're rich enough to buy tons of kodak, verbatim, or other high quality media.
Also keep in mind of this, I caused so much fuss that I probably made a CSR at Iomega get yelled at. It turns out that my media (cheap CDRW media) could only burn at 2x. So I was blaming Iomega for my mistake. But it wasn't all my fault, the drive burned at inconsistent speeds even on the same media.