[leap_ahead]

It basically amounts to two alternatives:

1) they make it intentional for whatever purpose - stop scrappers, prevent search engine indexing, pull in ads etc.

2) they make it out of incompetence - probably somebody with insufficient web development skills just used some popular JavaScript framework to quickly cook up a site

Now the majority of the customers won't care, but if you're targeting a professional audience, this will not score you any points. If you were a software development company hiring and I were to reply to your invitation, I would first go to your website. If I saw a blank screen in my browser, my first question to you would be why a serious company does have a broken site. Depending on what I heard I might skip you altogether.

Personally, I don't think there are any difficulties in doing a "text-only" version as you call it. That's how I always approach things - do a classic version then add some gradual enhancements. I can't imagine doing it the other way around actually.

And yes, you can call me out of touch with the times, but text pages rank higher and more credible in my eyes then all of the JavaScript toys I see around.