More tracking metrics for them to consume on mobile, I suppose.

Ditto. It's still an open question how open and accessible to end users the Internet will be. Anything browser-based still has that potential. Well, except on iOS where the browser doesn't permit augmentation.

Aye, had the same thought here. I'd've signed up to check it out. I don't own a mobile... Even if I did, I'd not download an app on spec. WebApp gives an opportunity to sell yourself with no additional buy-in.

If they're looking to capitalise on FB's data revelations, asking to download binaries is the wrong way to go about it. You need a no-commitment approach here.