I think you missed the point being made by the person you replied to. The only 10.04 install you should encounter exists due to ignorance and not due to upgrade cost as with a non-open OS. XP/Vista/7/8/10 don't get upgraded due to them being proprietary and having a single point of support (concerning OS level exploits).
So, 1. because there is a community outside of a major corp who are active, so it isn't a burden on Canonical.
2. yes? see 1.
Should any IT professional not have upgraded from 10.04? No. It's free to upgrade, unlike Win which, remember, isn't a single upgrade, licensing is per user.
You too are missing the point. The same people who didn't upgrade from 10.04 would probably also not take advantage of the Microsofts offer to upgrade to win10 free of charge, because <reasons>.
I am so happy that win10 patches are mandatory despite all the whining. In fact, I want them to take it one step further and adopt the ChromeOS update model.
So, 1. because there is a community outside of a major corp who are active, so it isn't a burden on Canonical. 2. yes? see 1.
Should any IT professional not have upgraded from 10.04? No. It's free to upgrade, unlike Win which, remember, isn't a single upgrade, licensing is per user.