Windows had no way of knowing if it was compressing "old" files that were in the \Windows or \Program Files folder, and with the advent of junctions and SxS in critical file and folder locations instead of mostly straight files like you would have in XP and 2000, this option really made little sense. Since compressing Windows files (especially ones with junctions to WinSxS) causes an inordinate performance hit on older machines, having the ability to compress files from Explorer as necessary, as well as the "Compress old files..." option could (and did, a lot of times) cause the disk cleanup UI to hang, it seems likely this was removed under the guise of "disk storage is ubiquitous and cheap nowadays" when in reality it was a pretty buggy option to begin with on large volumes and didn't come into the new century ready for a new OS model like Vista. Anyone who used this on XP on larger disks knows the hangs I speak of, and it appears that on Vista (and moreso Windows 7), this option is gone in favor of using Windows Backup or a 3rd party archival solution to remove old files rather than compressing them. If you have a client with a large drive full and want to compress data, the problem isn't the data - it's that you're storing too much on your system without using proper archival solutions. If you have a file server with this problem, you either didn't scale properly and need to add more disks, or you need to implement nearline and long-term storage solutions - compression is a BAD idea in most scenarios nowadays.