unlike apple making "under the hood changes" and charging $$$ for it. windows 7 is a legitimate new OS.
Lets compare:
Snow Leopard:
All user land libraries are now 64bit - those components which were Carbon have been re-written in Cocoa. Grand Central Dispatch isn't some clip on library that dangles to the side and is left up to the developer to include if they give a damn as with the case of ConCRT - GCD is built right into the operating system with everything floating on top reaping the benefits of it. Interface cleans and tweaks, kernel improvements, lots of new developer orientated features to ease development.
Compare that to Windows where these features are either included but never used, offered but are still in beta (ConCRT) or the customer is sold a dud and told they must shell out more money to upgrade - case in point being computers that were loaded with 32bit Windows Vista or retail copies of Windows Vista 32bit where the customer then has to spend another NZ$50 to obtain a 64bit version of Windows that should have come with the box - and Windows 7 is looking no better.