Regardless of the CSS, any time I try to enlarge text in any browser and it doesn't do it, I get frustrated with the browser, not the website. Their is no reason I can fathom why a browser would not do this. So yeah, I'd take it as a bug in Chrome. If it's giving you the option to enlarge text, and Chrome isn't enlarging, or zooming, then it's a bug.

Same on Mac Safari. Webkit bug?

Nope, the CSS contains

-webkit-text-size-adjust: none; /* Stops the iPhone scalling type up */

which has the unfortunate side-effect of preventing text resize in webkit browsers.