That seems like a perfectly valid excuse to me. All other things being equal, if it's more work to write an native app, why would you? And with the incredible improvements in the Javascript ecosystem, "all other things" are indeed quite often equal.
The other crucial argument, which was made in other comments, is that the advantage of JS is further multiplied by its cross-platform nature. Basically every device that matters supports it. I believe that makes the comparison to KDE4 slightly less relevant :)
I have to disagree with this. Creating a form which displays a list of users and another to edit their details is trivial in, say, .NET's winforms. With [PHP,Python,Whatever]/HTML/JS it's a comparatively painful exercise. No form designer, you have to worry about low level stuff like data binding, the default styling is too basic to be of use. It's a major step backwards, hence people being excited about Meteor (http://www.meteor.com/) - it's finally bringing back the RAD tools that we've been lacking for so long.