Modern smartphone browsers (at least on Android 4+ including the default browser), allow you to override the website's request to control zoom.
As it should be.
Denying users zoom on a web page with the viewport trick is stupid. Sorry, but it is.
Websites shouldn't "pretend" to be native apps. GOOD native apps that don't respond to pinch and zoom will allow font size change anyway - such as the excellent Falcon Pro Twitter client. Lack of zoom doesn't matter because I can punch in the font size and all is well.
(I'd love to write a bookmarklet to re-enable zoom)