Remasters: what and why

Could someone explain exactly what remastering does and why some remastered Cds like Dire Straights Brothers in Arms sounds incredible and others like Jethro Tulls Benefit sound as irritating as it always did?
Shortly saying, you can't make a honey out of dump. If the original master tape was done wright, than you can master and if neccessary, remaster with better quality.
Why: many times "greed." I have some remasters that are poorer sounding than the originals! They are not always what they are cracked up to be.
The other ingredient of the "remasters" is who is doing the remastering. Is it some guy that really likes the music or does he just do it for the sale. It really all comes down to his ear and taste. I find the Mobile Fidelity, Classic records, Rhino, and I can't remeber the group that did the CCR re-masters. But those lables seem to be putting out the best products.
Originally mastering referred to the process of transferring music from analog tape to a metal disc format used for stamping out vinyl copies. It involved the sequencing of songs, the setting of volume levels, touches of equalization and some limiting/compression. With the introduction of CDs the term grew to include the transfer from analog to digital formats. Today mastering has come to mean virtually anything having to do with the finalization of a record in any format.

There's only two good reasons to remaster an existing recording. Either you're changing the final consumer format or you think you can make it sound better than previous editions of the record. If possible the remastering engineer will go back to the original master tapes (not the original multitrack recordings, but the final two track mix) from which they'll make a working copy. Sometimes the originals are not available and a second generation or later tape must be used. There are even cases where no tape masters can be found and the engineers have been forced to use off the shelf vinyl discs as their source material. Obviously, the farther away you get from the original master tape the worst the sound quality. A remastered version can sound better than an earlier version if they are able to access earlier master tapes, use superior mastering equipment and/or have greater skill at mastering than the previous engineer. The remaster can also sound worst if these three conditions are not met.