This is exactly why people like George Lucas, James Cameron and Robert Rodriguez refuse to use film, and make all their movies on digitial. In the pre-digital age, everything was recorded on film stock, and over time, it would degrade, because it was made on plastic. Over time (especially if it is exposed to sunlight), film would get scratched, faded, and damaged. Just like your old photographs. Even ink on paper fades. This is why very old documents like the Declaration of Independance is kept under airtight glass (which makes National Treasure extremely implausible...but I digress).
So, what you are seeing as lines are scartches and wear and tear on the actual film stock. If you check out the special features on some restored films like The Who's The Kids Are Alright, they walk you through the painstaking process they went through to clean up the original film print, so they could make a pristine copy for the dvd.
Hope that answers your question.