I nearly always watch movies like that with one, two, three, or all of my grandkids... you couldn't be more right, it makes it MUCH better.
But it's also true that I enjoy them watching them alone as well.
It's probably most fun to watch with my youngest grandson simply because I don't always 'get' the joke... He never misses... and will be break out in hysterical laughter when my first reaction is more reserved, perhaps a smile... but as soon as he's gasping for air from laughing it all becomes clear to me.