[statictype]

Can't be security. From what I understood Web apps work in the browser but when bookmarked as home-screen icons, they don't use the new js engine (even though it's still running in Safari)

Benign explanation: some bug in safari

Tin foil hat explanation: Apple doesn't want web apps to be as good as native apps. This explanation kind of falls apart when you ask why they would bother boosting the js engine at all.