It's the drivers that are the problem. Sure, if you pick the manufacturer and model well, you'll have no problems finding Windows 7 drivers, but if you are like most people who walk into a store and just buy whatever's on promotion that day, you're probably screwed.
Plus, we're talking about adding an additional expense of around $100 for an OEM copy of Windows 7, which is ignoring the fact that the EULA terms were changed recently to exclude exactly that sort of use. All that when a single piece of free software can get you probably 99% of the way to what you want?
Also, if they format the HDD on the laptop, odds are they'll wipe out the recovery partition as well, so what happens after people get over their irrational fear of anything new and different and decide that Windows 8 is acceptable? Remember, everyone hated Windows XP when it first came out, giving almost all the same arguments you hear about Windows 8. It's slow, it's buggy, programs don't work, there are no drivers, everything looks different... The list goes on, but now people are clinging white-knuckled to XP just like they likely will be to Windows 8 in 5-6 years.
I've yet to find anyone who can come up with a single solid technical reason why Windows 7 is better than Windows 8. Every single time I ask, I always get answers that involve how Windows 8 looks different and people don't like the tablet UI. Which are all valid opinions, but they're opinions about personal taste, not about what makes Windows 7 a technically superior product. Also, Classic Shell will eliminate probably 99% of the personal taste issues people have, so I'm always left scratching my head as to why people want to go through the pain, suffering and expense associated with trying to revert to the previous version of Windows on a brand name computer. In a year or two everyone will have gotten used to the new changes and everyone will wonder what the big deal was before.