observation between os x 10.2 vs 10.4

Major changes in versions are just that, major. The overall system is considered in the design process and sometimes parts are compromised. There is always an effort to make everything better, but once you get to a certain stage, you can't start bleeding the brocoli. 🙂 There is always an end point.

10.0 to 10.3 became faster, as Apple engineers did a lot of optimization without adding too much to the +eye candy+ and feature set. Things like RAM requirements, not the absolute minimum but the recommended minimum, stayed about equal.

10.4 added a lot more features and, so it was the first release to of Mac OS X that did not run faster on the same hardware. And RAM requirements, both minimum and recommended, about doubled. However, on some Macs, 10.4 may have seemed faster because of better optimized video drivers. Others may report it is faster on their Mac than 10.3 was, because they just did a fresh System installation when they upgraded to Tiger (and their Panther System was not working OK but not 100%), or because they upgraded their RAM at the same time, or both.

10.5 added even more features and RAM requirements doubled again. 10.5 is definitely slower than previous releases on the same hardware, at least on the PowerPC side.

So I in my opinion, it is true for the four release of 10.0 through 10.3, but not true for 10.4 and 10.5.