Ignoring Modern UI does not make Modern UI completely disappear. Nor does it change the fact that Microsoft thought this was a good idea. Poor usability is poor usability. Microsoft messed this one up, and it will impact them and a lot of peoples perceptions of the future of Windows.
Nonetheless, for most people on this site using Windows, it makes sense to take the relatively simple (for HNers) steps to upgrade to Windows 8 and hide Modern UI, as Windows 8 provides various performance improvements over Windows 7, Modern UI notwithstanding.