There are programs like that.
I believe there is a Mac version of the Direct CD control panel that does this, but I'm not sure.
There is most definately an app called CDR Access, which lets you use a CD-RW like a floppy disk.
All but useless? Hardly. The best way to use CDRW's is in Toast. Erase, burn, use. Repeat.
Much better than like a floppy disk

Put all your files there, burn it, get a little something to eat and come back and its done.
Not dragging 650 megs of stuff over that could be comprised of 30K files, to the CD...
Not to mention CDRW's weren't designed for that, and that does waste space and take longer in the long run.
Cipher13