There's no point getting mad about changes George Lucas makes to the original Star Wars films anymore. They're amorphous blobs more than films at this point, and have been since Lucas started seriously tinkering with them back in 1997. And that's okay! The original versions of the films still exist, so you can always cling to that, but the new ones are actually pretty fascinating, if for no other reason than Lucas makes some very strange, subtle changes. We all know (and mostly agree) how weird it was to reverse the Han/Greedo scene (the infamous "Han Shot First!" battle cry of internet nerds for the past 15 years), but there were a lot of changes made, some of which have some seriously questionable logic behind them, and these are some of the most baffling.
This is extremely weird - George Lucas brought back the original actress who played Oola (the dancer at Jabba's Palace that became Rancor food), put her back into the original makeup and costume, and filmed a few reaction shots of her. Virtually all of the footage in the film remains the same, except for a few quick shots of Oola freaking out as the Rancor's preparing to devour her. It doesn't hurt the film, but it really doesn't add anything significant or noticeable to it. And that seems to be the point: to add some supremely minor changes that you won't notice as out of place.
The fact they brought back the original actress, put her in full makeup, and had her re-act the part is an extraordinary length to go to add a few shots no one noticed. To be fair though, she does look exactly the same as she did before, so the effect is as seamless as desired. But this begs the question: Does George Lucas stipulate in actors' contracts that they have to cryogenically freeze themselves for two decades after making a movie in case he wants to film additional reaction shots? I'm not trying to make any wild accusations here, but the evidence is pretty compelling.
It was always a little weird that Obi-Wan was able to shriek like a giant lizard. That's just not a "Jedi thing" we were ever made aware of before or since. And that's fine. I can accept that Jedi can impersonate big lizards whenever they feel like it, just the only time we've seen it was the one time it was useful to do so. Okay. Sure.
The weird thing is George Lucas decided "No, that's not the specific lizard impersonation Obi-Wan would do. Sand people aren't afraid of dewbacks. He would've done a krayt dragon!" Maybe that would've made sense if he wasn't also walking towards then, waving his cloak around like a psychopath. That's what they were running from - the crazy cloak man making lizard noises - not whatever particular species of lizard noise it was. Maybe old people shambling down a hill making dewback noises were known to be kind and non-threatening in the Star Wars universe? I haven't read enough of the Extended Universe books to be sure.
Why is the Empire using multiple giant lizards for transportation on this desert planet? If they were sand people, okay, I'd get it. Sand people aren't the most technologically advanced folk in this universe, and they use whatever is available to them.
But the Empire is not only technologically advanced, they are the MOST technologically advanced organization in the galaxy. They have a laser that blows up planets. They can have their giant Star Destroyers travel at light speed with no issue. But when they're looking for droids on a desert planet, they choose to travel by giant iguana? You have to feed and care for these giant, unwieldy animals that are difficult to control. Even a poor farmboy has a landspeeder. Why wouldn't they use one too? Odds are they have ones that are way better than Luke's, and would probably have tools to help find droids that would not be susceptible to bearded old guys waving their hands. If one or two Stormtroopers were using dewbacks it would be okay (maybe their landspeeder broke down or they were being punished for another terrible day at the shooting range), but the idea of this many Stormtroopers riding fat, slow iguanas is a little weird.