Mobile Safari requires external Javascript from another domain which is blocked or failed to load
Turning on the Developer Toolbar showed lots of JavaScript errors, specifically:

undefined, typeerror, can't find variable $


This indicates that $, the "root" variable for jQuery was not set and therefore jQuery was not loaded.

Further, the error ajax.googleapis....ery/1.7.1/jquery.min.js - syntaxerror - parse error showed that the cached version of the jQuery library was corrupted and this is the reson why jQuery's $ was not loaded.

Force quitting Safari and clearing the cache again resolved the issue.