Do movies that were put on dvd first, but then added to bluray have extra features, or does it just have a clearer picture? (b q) Also - If the Dvd had like two disc for example, do they put every single thing on Bluray too?
It really depends on the company making the Blu-Ray. Some movies have more extra features, some don't. Usually newer and more popular movies will be the ones with the extra features.
As far as if the DVD was a two disc set and do they put the stuff on both onto one Blu-Ray, once again the answer is it depends - doing things like that costs money so maybe they will, or maybe they won't.
Personally I remember when DVDs first came out and they made such a big deal about all the possible extra features, but in reality 99% of the time they were just ads for other movies that you couldn't skip, or a second audio track with commentary. I wouldn't be surprised if Blu-Ray ended up the same. The reason this happens is because it takes a lot of programmers a lot of time to make cool extra features, which would make the disc more expensive.