From what I've read on Ten Forums, you can do a clean install with the 10 upgrade. If this is the case, I doubt you'd have to install the OS you upgraded from to format as suggested. It appears the 10 upgrade will be available as an ISO to install it stand alone. I imagine that means when you go to get the upgrade, it scans for the model and license key of your current OS before it gives you the ISO DL code.
The code would then be associated with the equivalent level of OS (Home, Business, Ultimate, etc), and validation status (licensed, non licensed). I've also read that their latest scans of this type can as well determine if the license key detected is already in use, which may mean even if you have a cracked copy that shows a license key and the genuine MS software logo, you won't necessarily see that with the 10 install.
That said, I would jot down your current license key and the DL code, just in case you're asked for it when reinstalling 10. Note, in order to be able to reinstall, you should burn the ISO to disc. Just the fact that they're offering it as an ISO likely means it is in bootable format intended for disc.
http://www.tenforums.com/general-discussion/4755-will-i-able-do-clean-install-windows-10-a.html
Some are confusing the term upgrade with addon, since that was the way MS did their upgrades in the past. Things have drastically changed since then. They're not only listening to their customers more, they're even making this upgrade available to non licensed (pirated) copies, primarily to keep the Chinese on Windows, whom mostly pirate the OS.
Plus they have been drastically simplifying the install process of their OSes, which includes upgrades. You have to understand, with MAC OS (and Steam OS) being free, and so many people on Apple now, they can't afford to keep making things difficult for users, financially, OR technically.
I have no idea what they are. I install all updates except for language packs, Skype as I use desktop and all bing related nonsense. Never had a reason not to install optional updates. Seems silly not to have them.
After a recent format, when reinstalling W7 this time, I read through all the update descriptions and opted out of ones I thought weren't necessary, but SP1 kept failing to install. So now I have updates set to treat the recommended ones the same as the critical ones. There's very few I don't install anymore.
It's easy to hate on the bloat of Windows, but without it, we probably wouldn't have such mass compatibility with software.
It's a beta releasing in a month and a half 
I hope you are a patient man.
