Well, in my experience with HP/Compaq, they tend to have a lot of board level components fail. Either using cheap resistors, transistors, chipsets, or even the boards themselves. There isn't really anything that a person would do to cause these to fail rather than just bad/cheap components.
Dont get me wrong, they arent the only ones that are guilty of doing this, Dell got busted several years back for using cheap knockoff capacitors that had been copied from another company. The electrolyte formula that was used had been stolen, but little did the cap manufacturer know that it was a faulty formula that they were copying. But many many companies got caught up in this particular scandal.
Like I said, I am sure there are many out there that work fine and great, but repairing machines on a daily basis, I see more of these come into the shop than any other system. I will say that I like HP printers....