Here's the reason....
...Buy a PC - and and someone has pooed in the box.
It's not just Vista.
Every beige box sold is filled to-the-brim with third-party crippleware.
Each and every one of these programs loads itself into the system and leaves its hooks in deep. They nag you to buy them. And you know, deep down that when something goes wrong, one of these pieces of crap is to blame.
They'll be a half-functional virus checker that slows the system to a crawl.
There'll be some fancy 5.1 sound driver, that has to proclaim itself at every boot with a fancy splash screen.
And there'll be a half-dozen others. Crammed in by the box-shifter because the software companies have paid for them to be there. Sometimes they don't even work together.
Half of them don't even follow Windows user-interface rules. And if you want to hose them out, good luck.
It could be hours before you get on the internet, and when you do, each of them will want to start downloading updates.
Who would want this? How did the PC market get into such a state where respect for the customer counts for nothing?
The reason Apple is doing well is because it respects paying customers enough to not shit in the box.