Jonathan Schwartz makes the point that rewrites done just for the sake of a new language/toolkit don't make sense - something the entire industry collectively forgot about a decade ago:

Before I receive 2,000 email critiques, you should know my roots are in desktop software. So lest you think I'm coming at this from the perspective of a knuckle dragging big iron computer guy, that's not me.

As a software guy, here's a simple (though often irritating) rule behind user oriented software: The language in which a product is written has nothing to do with the value it conveys.Coming from the company that produced Java technology, that probably sounds a little odd. But it's a simple truth, especially when it comes to users: if the app's no good, it's no good, even if it's implemented in Java. Or PHP. Or Rails.

...

Because rewriting an app simply to use a new toolkit isn't creating value for consumers. Creating an application or service that delivers unique value is what captures users. And the internet gave some developers a tremendous opportunity to deliver unique value - by radically simplifying basic networking, enabling connectivity and community on a truly global scale.

Couldn't have said it better myself.