Actually, there's a lot more to it than simple 'key/value' binding, depending on how it's implemented. It allows you to build very live pages that are driven directly off your data model. Normally, websites build dynamic content using a templating system on the backend, but live updates need to be done in a horribly awkward manner using a Javascript builder syntax or manually gluing together things in JS. This avoids this problem and unifies it into one nice syntax.

I built a similar language like this powered a site of mine that was actually in production (well, Alpha) - and it was a huge productivity boost, resulting in far more interactive pages. (The site never got out of alpha, and never had designer love, so it's stale, but you can see it at http://www.magnifeast.com - try entering a los angeles address).

The downsides to this approach are compatibility (most libraries won't work out of the box), SEO, and performance problems for generating large pages (particularly in IE).

(BTW: this is a secondary account, I'm normally sshumaker - noprocast rule and all).