Anyway, I would like to hear why you think each 10.x is so different? more small programs? or structural change? if M$ sold their system like these 10.x increments price, at these 10.x's releasing pace, trust me, PC user will sue M$ to supreme court, LOL
Massive structural changes that have allowed better applications to be produced.
Enhancing the underpinnings of the operating system may not immediately bring any 'wow' factor. However, these additions, fixes, simplifications and reorganisations allow developers to create better applications in a quicker amount of time.
Tiger was *massive* for developers. CoreData, CoreVideo cocoa bindings, embedded SQLite, better integration of Cocoa, Carbon and Java. A quick glance through MacUpdate's listings reveals how these technologies have led to some great applications.
I've used OS X continuously -- every 0.0.1 and 0.1 update since 10.0.3. If you'd done the same, you wouldn't have any qualms about the worth of these updates.
Also, you've got to bear something very important in mind: OS X in its present incarnation is very young. Take a look at some screenshots of the first public beta (only 6 and a bit years ago) and compare them to what we have today. It's astonishing. Compare XP Service Pack 2 (MS's current desktop OS) to what was around back when OS X was in beta - Windows 2000. There's really not a lot that XP offers that wasn't possible in Win2K. As a Windows developer, there's very very few instances where XP offers features that I can't use in 2K*. Where's the innovation? Where's the value of XP if I can code Win2K to the same standard?
[edit: oops, yes.. I just remembered *one* thing XP gave me that 2K didn't... a few extra classes in the WMI interface. Whoop-de-do. The workaround to operate on 2K was just to tweak the registry directly. Not exactly a brave new world of features...]
The fact that Apple's not neglecting the guts of the OS is heartwarming. Too many developers view platforms as 'good enough'. It's important that Apple keep improving the core of the OS so that developers can produce better software.
On a final note, I can't wait to see what user interface designers come up with once they get their hands on CoreAnimation -- something which itself wouldn't have arrived if not for the work done in past years on Quartz, Quartz Extreme, and the Quartz Compositor.