Continuity mistake: In a scene early on where Mike is behind the video shop counter and Jerry is in front of it, the positions of the videos on the shelves behind Jerry alter from shot to shot.
Continuity mistake: When Jerry is talking to the woman in the video store after being magnetized, the videos on the shelves keep changing position. Keep your eye on the Lord of the Rings tape.
Continuity mistake: When Craig and his friends put the tapes on the counter, Robocop is on the bottom. Later it's on top. Then one of the guys sets it aside on the counter and in the next shot, Robocop is back on top of other videos.
Answer: VHS is data magnetically encoded on tape. A magnet will wipe them out. DVD/CD's are data encoded in plastic with a laser. Magnets won't hurt them in the slightest. Yes, the static was intentional, magnets can interfere with televisions.
Grumpy Scot