Quality system, make poor recordings sound better?


I notice that as I move up the audio chain, poor CD recordings sound worse and the good ones sound superb, should this be the case? Also I on any given day my system sounds different even with the same CDs. Any thoughts on this as well?
phd
Thankyou all for the great indepth answers. A few days ago my
daughters boyfriend brought over his IPod and connected it to
my main system. He was thoughtful enough to have downloaded
some of the music I like, new and older recordings. I thought
all the music played sounded spectacular. There wasn't that
big of gap in sound quality between older and newer recordings
that I experienced with CDs. Go figure. I think maybe I should
get an Ipod as a source for music.
Digital complicates things a lot in that there are unlimited ways any particular digital audio files may have been processed at various points in ways that have major effects on sound quality. The differences will no doubt be subtler
played on lesser equipment but more significant as the playback system gets better.

For example, there is much less difference between my best digital files and my worst(all lossless FLAC, a few converted from lossy compressed mp3 file download) played back on my Sangean WR-1 table radio, my least hifi playback device, though no slouch as table radios go, compared to played back at home via my main rig laying on teh big OHM F5 speakers. I have a half dozen or so other options in place for playing back those files concurrently. The others all fall in the middle somewhere in regards to overall sound quality.
the recordings must have sounded good to someones ears . more than one set of ears will hear a recording before it is pressed . how does a poor recording get let by ? cheap radio shack equipment in a major studio ?
bands can take years in the studio to make records. you think they are going to let crappy produced music out ? There has to be some kind of quality control. Some times it gets redone by a different producer if the record company or artist is not happy with the final product.