My personal opinion is that trying to conceal Anakin becoming Vader is pointless, because you can't get around the fact that Obi-Wan lies to Luke about Darth Vader killing Anakin. If you try to cut out Anakin's final transformation from ROTS, then it makes it look like Obi-Wan killed Anakin, lied to Luke about him turning evil, and then blames it all on Darth Vader who to the viewer's knowledge wasn't even around back then. Basically, instead of us getting the sense that Obi-Wan lied to Luke for his protection, it makes it look more like he was being an ass.

On a more personal notes, seeing Anakin turn into Vader is one of the reasons I went to see Episode 3, and the same can be said of a lot of people who went to see it. I mean, it was one of those things I wanted to see since I saw Return of the Jedi when I was a little kid, right along side Anakin's duel with Obi-Wan. I can understand that some people want to preserve the shock of learning that Vader is Luke's father, but I just don't see how that can be done without undermining the purpose of the prequels.

I mean, if people are that intent on making Star Wars viewable in chronological order while keeping all of the surprises and twists of the classic trilogy fresh, then you may as well cut out the downfall of Anakin altogether, which really kind of begs the question: why even have prequels in that case? To paraphrase Yoda, "dangerous this path of thought is." I honestly don't think ROTS can be the best movie it can be if it's going to lose one of its most iconic moments, which really the entire trilogy had been building up to.