It was all about being in the wrong or right place at a specific time. Yes, some truly insignificant Jedi survived, but think of how many of the Order's greatest fell. It was essentially a matter of luck. Obi-Wan himself would have died if Boga hadn't protected him. It's all a matter of circumstance on who survived and who didn't.
And to all of you saying that too many Jedi survived, I disagree. Yes, it was a moment of glory for the Sith, the culmination of a thousand years of hiding and plotting, but think of how many Jedi there were in the galaxy at that time. I've seen numbers vary from anywhere between 10,000 to several hundred thousand. When you really think about it, how probably is it that all but two Jedi would die? Think of how many just happen to be away from their troops; think of how many just somehow manage to escape. Even if you figure 99% of the Jedi were wiped out, you still have 100 Jedi roaming the galaxy (and that's going with the low estimation of 10,000). After hearing that information, doesn't a few dozen surviving Jedi sound not as bad?