Gremlins was a hit when it came out and has remained popular ever since which doesn't scream cult to me.
Cult is usually a film or show that remains largely ignored upon general release but gains a steady following through word of mouth or (in this day and age) internet forums which then means the media re-evaluates it and declares it the best thing since sliced bread.
This only made it on mainstream T.V here last year which is when I caught it (in fact I bought the boxset a couple of months back and I'm halfway through season 3) and everyone with half a brain was hooked. I am sure it took a long time to catch on in the states too.