The reason that Apple does not allow other engines in iOS is simple: it keeps all performance and security issues restricted to a single code base. That's good for users too. Considering that browsers implement the gross of their functionality (rendering + javascript) according to standards, there is no reason to have two different platforms that do exactly the same thing. As long as the standard is not owned by any private individuals, this is beneficial, and the same would apply to Windows tablets.
That said, leaving everything on the hands of Internet Explorer scares me, so maybe this fight should be supported :)
Why wouldn't Microsoft be able to use the same excuse then. There are always advantages and disadvantages. The questions is what is the compromise you're willing to live with?
Apple, much like the US Government thinks security trumps everything, including individual liberties, "for their own good".
Indeed they could, I just said that. This lock might force MS to make IE's engine as good as WebKit. I don't see any problem as long as the standards are kept open and the engine doesn't belong to a single entity.
You got the lock-in strategy backwards. It exists to allow the incumbent not to improve their products while maximizing their profits because they don't have to compete.
That's how IE6 used to be, too. But because they eliminated all their competition, they didn't have to advance it anymore. It was cheaper and easier to keep it the same.
Why restrict that reasoning to browsers on iOS? You could apply the same reasoning to restrict OS X to only run Safari. Or only allow iTunes for playing music, since there are standards for encoding audio and organizing playlists.
The fact there are browser standards is not a reason to only have one. Competition among browsers leads to improvement in standardized areas like scripting and rendering, and browsers can offer a lot of other functionality that benefits users.
That said, leaving everything on the hands of Internet Explorer scares me, so maybe this fight should be supported :)