08-01-14: AustinbobKijanki's response is of course correct, as usual. A second set of reasons why playback of a ripped computer file may sound better than playback of the corresponding CD in a CD player, however, relates to jitter and to coupling of electrical noise from the CD player's transport mechanism into its other circuitry. The magnitude and character of those kinds of effects will of course be dependent on the design of the particular player.
I also think CDs ripped to lossless files on FLAC can sound better than the original CD, my theory being the error correction while ripping produces a more stable file (but don't have a shred of engineering background to prove this).
See my post here for further explanation, although that thread addresses sonic differences between playback of an original CD and playback of a CD-R copy of it in the same CD player. Obviously, a comparison between playback of a computer file and playback of a CD introduces many additional variables into the mix.
My understanding is that a CD that is in good physical condition will have very few if any read errors that are not perfectly corrected during realtime playback. So I would expect that typically those noise and jitter issues will be of greater significance.
Regards,
-- Al