There are several 16x burners out there (Pioneer DVR-108); most of them are DL, too. They just started shipping recently, so I don't see why you would expect to see them in Macs. Slot loading drives are just now get to 8x, so laptops and the iMac can't do 16x, yet.
In any case, if you want a 16x burner, go out and buy one, just like every PC owner that bought their machine before the new drives appear. Why do you always make these topics sound as though Apple has failed us somehow?