Except for one big difference -- today, I or the company I work for, doesn't have to own "the mainframe". Basically its a return to the "mainframe" with the cost and exclusivity. That is a huge difference.

In the 70s you had "computer bureaus" that owned the mainframe that you would rent time on by the hour. A lot of the early MUDs ran in spare capacity on these. Exactly like the cloud...