Whether this document works or not, is subjective.
For instance our Shared Servers have multiple hex-core processors with NginX, Varnish-Cache & Apache, 32GB or more of memory, with various DDoS and Brute Force avoidance technologies.
I would say that unless you need some software or technology not offered by such servers that you don't need a VPS, as access to such technology can be yours for much less than via a VPS.
If you want to do your own system administration, then yes, a VPS is a superior offering, but if you don't, you should avoid VPSs.
I can say that the number of VPS owners who get themselves into a mess and need an admin to help them get their machine functional again after a "do it yourself" gone wrong, greatly exceed the amount of support tickets for shared/reseller services despite the number of shared customers being hundreds of times higher, as they are administered by supported by an experienced NOC team, who've set every up as it should be.
You are right though, that VPS is a progression from Shared/Reseller hosting, as often when a shared site gets too popular and takes "too much" share of a shared server we do encourage the site owner to "upgrade" to a VPS.
But if a site is so popular that it needs this kind of upgrade the customer often wants a manged service as the service has become too precious to "DIY".