It certainly depends on the movie and the scene. When a DP needs to shoot something in a dark setting, there are a few ways to achieve this. They can open the aperture, lengthen the exposure OR boost the ISO, or film speed. Boosting ISO is, essentially, using a film with higher light sensitivity or using equipment which mimics higher film sensitivity.
The caveat is that high ISOs will introduce more film grain to the picture. Sometimes this is a necessity because of the low light situation. Sometimes it's a stylistic choice.
I suspect that you were watching a scene where the DP chose a high ISO b/c of the lack of light. It may have been enhanced by your sharpness settings on your TV. As noted previously, a hi-def version of the film may enhance the appearance film grain as well.
