I think it is a lot to do with the sardine effect too.
If a video has lots of views, then folks will think 'It must be good, so many people have watched it' so they watch it.
That's what I think anyway.
You can actually 'buy' views directly from youtube aswell. By setting up an advert, using one of your videos as the ad. It then pre-roll's on suited other videos and you pay if the punter watches it for more than 30 seconds, and you get a n extra view count.
I did it a while ago and 1000 views cost £6 or something. I was hoping to drive people towards the subscribe button with it, but managed to net only 3 new subs!!