how is it that each dyno ca be so sophisticated, and account for so many variables, yet one dyno will not match up with the one next door?

Yes it sounds pretty stupid doesn't it?

Has anyone actually had their car dynoed on two different dynos and had two very different results???

There was a thread about this not that long ago.

The dynos themselves are very accurate, BUT there are lots of variables that can change the result. Many dyno operators dont know, cant be bothered, or play with this to give high or low readings.