Redbook: only 1/4 of the master tape???

I've been listening to SACD exclusively for a few months and have just gone back to some CD listening. It was more disappointing than I had expected, and my Marantz SA-14 ver.2 has quite good CD playback. I read on another site that redbook CD can only hold so much of the master tape, no matter what the resolution, and that the information must be compressed, (too polite a word--I would say condensed), to almost 1 out of every 4 samples to fit on the old format. Is this true, and if so; why even buy a better resolving CD player ($$$) when it can only lavish quality on basically a skeletal representation of the master tape?