A real counterpressure bottle filler will let you purge the bottle with CO2. Then you pressurize it to the same pressure as the keg (I like to overpressurize it at 18-20 psi). Turn off the CO2, turn on the beer valve and adjust the pressure relief valve for a smooth fill. When full, turn off beer valve, let out more pressure from the relief valve, remove CPBF and cap on foam.
I bottle using exactly the method that Kai uses...a cobra tap with a tube jammed into it... and it works great.
As far as purging the bottles, I manage to do that too...I have a manifold on my co2 tank connected to another cobra tap that has a stopper attached...I give each bottle a shot (usually 6 at a time) then fill the forzen bottles with the nearly frozen beer, then cap 'em. Works great, it retains the carbonation level I like, and I have subsequently kept beers bottled that way for a year or more with no problems whatsoever.
The Beergun and the homemade CPF's are both great, but by no means are they necessities for bottling up to a case or two of beer at a time.