The purchaser does get a CD that can be used to reinstall Windows.
After a fashion, yes.
However, it also installs whatever else the vendor wants to install.
Is that it?
Pretty much.
It's not really a reinstallation of Windows, just a restore, something like System Restore that's built in to later versions, but more complete. That's the best I can compare it to.
It wouldn't reinstall Windows, etc., to a completely blank, new hard drive?
Beyond that, why did you insert (hopefully) up there. 
There must be something more to that....
Because it's not a full reinstallation, it doesn't always help.
I know a guy who had soem major issues, he used the restore disk and it didn't help at all.
Some kind of conflicting software/hardware I think, a full XP disk sorted it out though.
And sometimes the restores go wrong too.
Doesn't sound good for the vendor.
They'd have to do something for the customer.
P.S. I was lucky enough to get a full Windows disk with my computer, but this is getting rarer nowadays I think.
Definitely. Some vendors don't even ship a restore disc with their computers but uses restore partitions instead. They usually do include a piece of software that allow you to burn your own restore discs, but still.
It gets worse and worse . . .
Especially as many less savvy people don't know how to burn a restore disk or why they should do it.
What is the logic behind not providing a Windows disk?
it can's possibly save them any money.
That's probably it - money. One way or another. It is usually the motivating reason for anything.
I bet you are thinking that the CD itself can't cost that much - and you'd be right.
But suppose you owned the PC factory, and are punching them out and boxing them up, one after another. You've got a zillion CD pressed, and insert one in every box, right?
Along comes a software update.
Now what? Pitch all your copies? Get new ones? Let alone keeping it organized. Somehow I bet that there is labor involved in it, and the cost of labor adds up real quick.
