Actually, you know not many people pick up on this, but near as I can tell, Jabba was not based on Tatooine at the time ESB was made, and none of the heroes knew where he was.

Think about it: Lando says, they'll find Han, and sets off to do so. Why would they need to do this if Jabba is just sitting around on Tatooine?

Luke says they'll meet on Tatooine--but he doesn't say that this is to rescue Han. Its just a rendevouz point. Its out of the way, and Luke's old haunting ground. Lando is taking off to get a head start on tracking down Han, and in a few days time they are going to have a secret meeting on Tatooine to regroup.

Jabba is on Tatooine in ANH, but that's because its a spaceport and he had to track Han there to shake him down for money; there's nothing that indicates he was indiginous to there, anymore than Greedo was. They just had been able to trace Han while he had a brief stopover. Because if Han was trying to avoid Jabba for fear of his life, why would he be hanging out around the corner when the entire galaxy was open to him? That's what makes the Jabba element in ANH so unexpected to him, that even when he's hiding out in a remote desert planet his debtors still catch up with him.

It's interesting to consider the possibilities of the ESB climax, where Jabba is unknown and has to be tracked down, with a Tatooine rendevouz to regroup after Luke is healed.

Luke: I'll meet you at the rendevouz point on Tatooine...Good luck you two.

Lando: Princess, we'll find Han. I promise.