how is it obvious, users are still working on pc's ranging from win 2.1 to win XP, Not sure about registry's in pre win 95 machines but it makes a differance, work on an NT vbased machine compared to 9x system big differance.
Of course an NT based machine is very different from a 9x machine but most "tweaks" are mostly the same, i.e. defragging, removing spyware, temporary files, cleaning registry,...sometimes the way you have to do it may be different.

I don't think he's still using win 2.1 , heck you never know, sorry for that sort off inappropriate comment :
isn't that obvious nihil?