I'd also like to put my hand up for getting the wrong end of the stick here.
Fair play mate. Now get reading, and start asking VM questions. 😄
Economy of scale (sort of), yes VM or any ISP could do 'X' but doing this would cost 'Y' and only 'Z' percent of users would notice anything anyway, and probably doing so would result in about 0 increase in subscribers, it's not worth it!
Annoying, but to be fair VM is a business which exists to make money (as indeed do all businesses), so why spend X if you are going to make less back?
Let's be honest here, what percentage do you think of VM users, use the connection to download mostly cute cat videos? Do they care if it's using D 3.0 or 3.1 or 4.0? can I see my cat videos? If yes, then all is OK! Upstream issues, what's that then?
We all know that DOCSIS has issues with upstream, simply because of historical issue of how it works, but do you really think that the majority of customers care less? - it works (mostly); so fine*
* OK I don't personally subscribe to this viewpoint, but I do know how businesses work!