Developers would simply instruct users to turn off UAC (as they told users to run as administrator with Win2K and XP) rather than fix the problems
Therein lies the rub:
What I consider a "problem" and what Microsoft considers a "problem" are two radically different things.
Microsoft made this bed: To do anything useful for many years developers simply had to modify the operating system, leading to untested combinations, DLL hell, degradation of systems over time, and many other problems. Now, instead of providing a clean, well-documented new way to do things right - which they failed to provide in the first place - they just make it harder to do the old things, leaving us to discover ways to work around the arbitrary limitations (not to mention copious magic) in UAC.
I normally support Microsoft and I realize that without Windows the state of computing would be vastly different (and quite likely far more primitive) today, but this is one area where it really shows that people with IQs less than 100 are designing the system.