Why does ipad open mobile sites and not full sites

You can't change it, it is how Safari reports itself. There are other browsers available in the App Store that will show the full versions of websites e.g. Atomic Web (http://itunes.apple.com/app/atomic-web-browser-browse/id347929410?mt=8) has a setting where you can get it to report as Safari Desktop, IE, or Firefox

It's all down to how the web site you're visiting has been programmed to handle mobile browsers.

Some websites have been programmed to automatically redirect specific mobile browsers to alternative versions of the site.

Either you can use a different browser as suggested above, to 'pretend' to be a desktop browser, or you can contact the website owners and request that they treat iPad visitors as desktop visitors and don't show them the mobile site.

On the favourites page (no page selected) there is a button in the bottom left hand corner marked "private." Press it and the BBC News full site will be selected rather than the mobile site. This may work for other sites too.