I love this topic because I always get to mention the Autobahn. No speed limit and half the traffic fatalities per mile as US interstates, all because the slower people keep right, and allow the faster people to just pass.
I freely admit I generally exceed the speed limit (although usually by more like 5MPH), and I get annoyed when we have five or more lanes through our city and people are driving below the limit in the center and left of center lanes. Someone is in the "proper" lane if they are generally passing people to their right and being passed on the left. At the same time, I don't feel like I should have to get over and go slower so that the person behind me can exceed the limit even more than I am. If it's not going to slow me down, I have no issue moving over to allow a faster driver to pass. I promise you - if you want to go faster than I'm going, I really don't want to be in your way, but you have to give me reasonable time to pass the people I'm passing.
The problem is most people hate being passed, and think the people passing are jerks (instead of simply not caring, which we should all do more of - worry about yourself). I think it has to do with transactional analysis. I often drive in off-peak hours, and use cruise control (not autopilot!) because it actually helps me pay more attention to the road without worrying about driving a consistent speed.
It's true that it seems like people will speed up when passing.... and often slow down after they pass you. What I've observed is that it's almost always the person being passed speeding up. They may not even realize they're doing it - it's probably only millimeters of difference on the accelerator, and then they complain the person passing them slowed down. The vast majority of the time I'm passing people - using cruise control - they speed up to match. Maybe they feel like if they are being passed then they are going too slow. I think more often people just don't like "losing" the social interaction with others on the roadway. All I know is that it ends up causing a lot more traffic problems because you then create rolling roadblocks, causing people to have to change more lanes to go around. For me, I'll often speed up some more - and if they speed up to match, I'll drop back to my original speed and get behind them... at which point they generally slow down. Quite frustrating, but I don't want to be the person blocking traffic.