This is a bad way to count.

Imagine an organization which wants to buy Google's package for organization. Perhaps some government body. And that body has a regulation that requires certain accessibility features from services provided by contractors. So, even if very few, or even if nobody in that government body needs good accessibility, the IT will not buy a service from Google because one day someone will come and sue them for buying stuff they shouldn't have.

So, it doesn't matter what fraction of users actually needs the "basic HTML" view. The new one sucks from usability perspective, and especially from accessibility perspective. If they cancel the better version they have... well, I'd be all for suing the government agency that decided to use GMail.