I think Mike is on the right track with this in that pulling the bits off on a PC using error recovery produces an output that has all the bits which can easily be buffered into memory. Normal CDP's have error correction and interpolation and they will guess at the missing bits and insert them into the data stream if the laser doesn't pick them up.
In addition, even though the circuitry may be relatively jitter free and reclock the data it seems to me that having the laser pickup constantly hunting for the track when the disk is spinning at 500 RPM would generate timing errors pretty easily and being that Red Book CD's have no error correction codes as part of the data it doesn't take much to make the interpolation mechanism kick in. 'course I could be full of hot air, that wouldn't be the fist time.
Now, if they would put in large enough buffers on CDP's and use an algorithm that reread sectors when an error was detected there should be little or no difference between the data stream from a stand alone machine vs the data stream from a computer. Of course most folks don't want to wait 30 seconds for a song to start after they hit play.