The Hard Disk Makers Won
Now it is obvious why Apple’s Snow Leopard will take up less space. It does so by redefining the base value of storage from base 2 to base 10 counting. A MB has gone from 1024 KB to 1000KB. It may very well be the proper way to do it to be consistent with metric measurements, but it would make a lot more sense for Apple to simply rename units to their proper ones – MiB, GiB, etc.
Hard disk manufacturers have been cheating people out of storage for years by redefining the storage units to match with the metric system, even though computers work in binary. Everything else listed as a megabyte was really mebibytes. Other than the Finder, I expect other pieces of Mac OS 10.6 to use the more traditional definition where multiples of bytes are done with base 2 and not base 10.