I think you pretty much nailed it there Geoff.
If you're genuinely faster than the guy in front, you should be able to get past cleanly.
If you're racing with someone who's actually up to the challenge ie. you're swapping back and forth every lap with someone of similar speed and skill, then a bit of elbow or whatever shouldn't be a prob.
If you feel the need to take out the front wheel of some poor guy who's toodling around the track, or yell at him as you pass, then you're a friggin idiot.
As far as "block-passing" is concerned, from what I understand, the idea is to take away the oponent's line and make them slow/stop, not take out their front wheel.