Having come from a few startups and many more random experiments - most mediocre failures, I'd tend to agree that the web allow for much more initial testing and product validation (depending on the product and industry of course).
Gabor Cselle wrote an excellent post a few months back titled "The Biggest Problem in App Discovery" ( http://blog.gaborcselle.com/2012/10/the-biggest-problem-in-a... ) that every new startup with a basic MVP app will face (heck even with a fully polished app it's hard).
The point that needs to be really illustrated is that the web is still critical and regardless of the language used, will provide you with a suitable platform to test, iterate and improve before investing time trying to compete for minds, hearts and wallets on mobile.
