While those three examples are a fine and damning view of "must use the latest cool-toy web-dev trinkets" development approach, I'd remind you strongly of the survivor bias...

I suspect a quick poll of HN members could turn up tens of thousands of failed web startups, both using modern MVC/Ajax/Web2.0/Cloud/buzz-word-de-jour techniques, as well as hacked up in Perl/CGI or duct-taped to the side of a Wordpress install.

I'd bet the cross section of new or old technologies used to create a web based startup is not at all correlated to the success or failure. If the founder(s) are the sort of people to get the _other_ few dozen (or hundred) important things about launching a new business right (or at least mostly closer to right than wrong), then minor hurdles presented by "legacy" programming techniques are unlikely to have make-or-break effects on the business outcome.