Yeah, I know that. But I don't know why Gmail doesn't set it.

What BSeward said: The meta tag means the site launches full screen in its own instance of Safari – so any outside links clicked cause a switch to the main Safari app.

Google probably assumes email is closely tied with browsing.

I guess they might assume that, but I don't think it's true.

I think I click a link in ~5% of emails I read.

And even in that 5%, the time it seems to take for it to exit a full-screen HTML5 app and load Safari seems to be about the same as the time as it takes for a new tab to open when I open a link in the Gmail app (already in Safari).

Wouldn't your Gmail session lose its state when its browser is shut down?

If only there was some way to run two applications at once...

Oh. That is true. They could get it to remember what page you were on by storing your location in the persistent key-value store whenever you navigate and then putting you back in that place when it starts up. But as it is, it even remembers your location on the page and zoom and such.