Which browser? What about people who change their UA string?

If there's a case for not hiding them on the device because of the use case, I'd say that's the right place to do it.

Having said that, the browser should be consistent with WEP/WPA key entry etc. And I can see this being one of the low-level things in the hallowed "UI Spec".

Perhaps Greasemonkey would be a better approach?