Golden411: I do believe you are correct about people voting only within their categories + best picture.
I know that they've attempted to have people watch all the nominations, but if someone is actively working, would they have time to view up to 10 movies (just for best picture - the max # that can be nominated) that are usually at least 2 or more hours long each. Heck, I don't work in the industry and I do have free time, but I don't even get to the theater to see many movies and even when I'm home, I seldom watch movies via DVD because I find myself doing other things while watching the movie. So, I can't imagine watching that many movies in the time between the announcement of the nominees to the voting deadline. ...and there's my problem that there are some movies that I just don't want to watch - although an Oscar nom might give me 2nd thoughts.
I do believe that studio's also re-release movies into theaters closer to Oscar time to remind the Academy that the film was out there - especially if it was released earlier in the year and the studio feels that it was Oscar worthy.