I think part of it is that there is now such a massive variation in the abilities of cyclists on the road. Ten years ago, you only got decent club riders or couriers. Now there are Sportives every weekend, more people are commuting by bike, in London you’ve got the Barclays Cycle Hire scheme and the riders using that vary wildly from competent to utterly insane.
So drivers simply don’t know what to expect or how to cope. A decent rider on a road bike can clip along quite happily at 20+ mph but the driver has just overtaken some dappy old bat on a shopper doing 5mph. It’s that fear of the unknown coupled with the very fact that you being there has caused the driver to have to do something other than sit there in bovine indifference – you’re an uncontrollable aspect of that drivers life and if the driver feels threatened or confused by you, some of them will react in the way we’ve all seen from the videos.
It always astonishes me though that drivers get so precious about their cars, bemoaning any slight scratch on them but they’re willing to slam it into the side of a cyclist… 😯