The problem with Epic adventures, is that they almost have to be custom made.
Depending on the party composition, the challenge level will vary greatly. A party comprised of a 25th level cleric, sorceror, fighter, and barbarian, might be able to swiftly take a PARTICULAR 25th level encounter, but the same encounter might be very hard (tpk) for a 25th level druid, rogue, paladin, and ranger. Yet, the situation will be reversed if they encounter a totally different, but still 25th level encounter.
The same thing happens at low-levels, but as the PC's get higher challenges, that fact becomes more and more important.
It would be very difficult, for instance, for a game designer to come up with a 40th level adventure. In the back of the adventure, instead of reading "suitable for 4 to 6 players of levels 38-43" you might read "suitable for 4 to 6 players of levels 38-43, Cleric and Bard necessary".