The question really is, who is responsible? Mobile Safari for not rendering properly or ning's responsibility to work around the weirdness of every mobile device.
(Did I give away my bias?)
Changing browser won't help - they all use the underlying webkit engine in iOS. It is how Ning renders under mobile webkit that's the issue.
You could try using the mobile version of the site - http://retromaccast.ning.com/m or using the Ning app.