[kahawe]

Taking a stab in the dark here but I am wondering how important users messing with their boxes are there.

I assume more "beige boxes" are either bought together from cheap components and been assembled by the users themselves or are generally cheap noname buys assembled by who-knows in the shop or maybe they have been modified and/or over-clocked by enthusiasts thus making it more likely to fail - whereas the typical users who buy "brand name" PCs or laptops are not going to mess with them and they can rely on at least SOME standardized quality assurance and control.

[osivertsson]

I agree with you that many factors need to be considered here that isn't mentioned in the paper. But they mention in section 5.3, "Brand name vs. white box", that "to avoid conflation with other factors, we remove overclocked machines and laptops from our analysis."