You should remove the word "mobile" from the MobilePhoneUserAgents string, that was a bug and that fragment exists in iPad user agent so having that will make iPad use the mobile phone skin when iPad really should use the main site skin.
The only case where iPad would use Markitup is older ipads, anything using IOS5 or higher Safari does support using the real wysiwyg editors like CKeditor. You can make it not load markitup by adding AssumeMarkitupIsLoaded="true" on <portal:ScriptLoader in layout.master but for older devices that will still result in just using a plain text area.
Note that in viewing your site it looks like you have <add key="CombineCSS" value="false"/> which is making it load a whole bunch of css files. I recommend set that to true or else combine all the css into one file yourself and then just list that one file in style.config. All those separate http requests for separate files is not good for performance.
Hope that helps,