Well, I remember the same problem with vinyl...I have a few records that I could not put onto a standard tape! As in 23+ minutes per side!(One Jean Redpath comes to mind)..and I have a few albums that I discovered were only 12-14 minutes per side! I simply assumed that there were varying degrees of generosity in the music business... I know that re-releases, like Sandy says, are a special problem...but there ARE ways to generally offer good value...especially with the higher prices of CD's.
Once, when CD's were fairly new, I asked Bruce Phillips, who was offering his first CD, if the prices were truly reflective of cost, figuring that if anyone would tell me, HE would! He said that, no...the manufacturers 'could' have sold them cheaper, and he,(Bruce) personally, hated to see the price jump, but that he had little control over the final cost...but he did put a generous number of songs on the disk.
When you can buy bargain CD's for $3.98 and even burn your own for a buck or two, you KNOW that you are paying for some artists/producers/manufacturers notion of "what the traffic will bear" in many cases. Yes, I know...some music is being pirated and tapes are being traded and MP3 is eating at profits in some areas, and many artists/producers feel they need to get extra up front to compensate...and fewer songs per disk is one way. But $15-$18 is a LOT of money to me right now, and I do suspect it does not have to be that way!