OEM EULA only states you can't put it on another pc. No stopping you from reinstalling OEM.
The OEM disk is not an install disk but a restore disk. You can certainly use it to restore the original OEM image but that of course leaves you with all the crap that you wanted to eliminate in the first place.
I always do a clean install regardless if it's a PC I built, or one like my HP laptop. I see no reason to pay for something as easy as doing it yourself.
That's definitely a better option but that assumes you have a separate install media for the OS which most folks would have to purchase separately.
For those who want to get rid of bloatware on Propriety machines (dunno why anybody 'd wanna buy one), head over to Majorgeeks WWW Link and get Decrapifier.
I did actually use this but there were a number of items on the machine that weren't on the listed apps. The other point in my case was that HP embeds a bios/driver auto update mechanism that is threaded throughout the system. The only way to get rid of that was surgical extraction from the registry and deletion of a multitude of startup items.
As far as why anyone would want to buy one it's most likely that they just don't know any better or are afraid of going to someone like ibuypower or newegg to build their own. In my case I was just being lazy as the last time I had purchased an OEM machine was before 95 was even out and all you needed to do was take your hard drive from the old machine and put it in the new one and you had everything just as you had on the old machine. You might have to change a video or other driver but things were far simpler. Anyway next machine I buy will definitely *not* be from an major OEM.