Earlier quoted context omitted.
AJAX isn't why Gmail became successful. What set Gmail apart from its competitors was the huge amount of initial storage you got (1 GB for free at a time when Hotmail offered less than 10 MB for free), a higher maximum attachment size (25 MB compared to the webmail standard 10 MB), Google search, and conversation view. All of which, by the way, worked with the AJAX-free basic HTML view.
I had forgotten how big a change conversation view was compared to other webmail. Also for what it's worth, I still use the Basic HTML view because I find it a better experience, so AJAX was definitely not the selling point for me. The 1GB thing was a huge factor though.
To me it just feels like basic view is just v1.0 from 2004.