I'm curious, why?

If you're OK with having a price tag and sharing restrictions on digital content in the first place (most likely involving some kind of DRM), why not let them set different prices on different versions of it?

I'm on the fence myself. I dislike DRM in principle, but movies and TV shows need to be funded somehow, and I hate ads, so I'm happy to pay a reasonable price.

I feel the same, however the way I see it, the price you pay is to access the content, the delivery medium should be up to me (within reason - I'm not expecting a bluray or dvd release without having to pay shipping costs etc).

Personally I am paying for the experience of seeing a movie in the theater, and I don't like 3-D. Last weekend I wanted to see Resident Evil. The local theater has seven 3-D showings times, and only two 2-D showings. If a theater is only going to mostly offer 3-D showings, I might go of the price was the same. Since I'm not interested in paying a premium for 3-D, I simply won't see the film if there isn't a 2-D option. If it is reasonable to not offer the product I want to buy, then so be it.

SD & HD I can see being the same price but 3D takes way more effort to create than 2D.

I found that BBC sell HD content for [~40%] more - which to me is crazy if it's more than a few pence more, all the people are paying for at the sale end is the cost of a little more storage. In a way the SD should be more as you have to transcode it, they're filming it in HD already.