The StackExchange sites that have a mobile theme seem to include the following markup in the head (I only checked stackoverflow but I'd imagine the other sites with mobile support do the same).
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=0"/>
This is really really bad for accessibility. There's nothing worse than doing a pinch to zoom in your mobile browser only for nothing to happen. It's not merely annoying, it makes Stack Overflow basically unusable on a mobile device for vision impaired people.
I know that there's a link to the full site on the mobile version, but because the text is so small and I can't zoom it, I was unable to find it for a long time.
Please loosen up the zoom restriction.