Sites need only be more specific with their detection code.
The HTTP_User_Agent for the iPhone is:
Code:
HTTP_USER_AGENT=Mozilla/5.0 (iPhone; U; CPU like Mac OS X; en)
AppleWebKit/420+ (KHTML, like Gecko) Version/3.0 Mobile/1C25 Safari/419.3
Many sites may just be looking for AppleWebKit, if they are, they will need to switch to more specific identifiers.
If you come across a site that does not do this when using the iPad, you may want to contact the webmaster with that information.