Films are often re-mastered for DVD. With some films some people complain that brightening up the film spoil the original gloomy, low-budget realism effect (like with Withnail and I), but with many films the DVD transfer improves the overall visual and sound quality of the film.

With PowerDVD I think it's designed to have "Vivid" as a default mode, I don't think the Theatre and Original setting are actually "original" they just tone down the vividness and brightness a little.