siteSpecifciQuirks is on by default on Mac (?) but off on iOS. It's exposed in the Develop menu so web authors can test with quirks disabled. We may need to add an iOS switch for this too (or have the web inspector do it). Also the WK1 pref is very confusingly named "WebKitUseSiteSpecificSpoofingPreferenceKey" and initialized with @"0".
I do not think this is valid anymore. It is currently consistent between mac and iOS. Simon, I will close it but tell me if I have been too hasty.