I think one of the biggest things that sold Boba Fett as a popular Star Wars character was the voice. That chilling voice from the original Empire Strikes Back was a large part of what made Boba Fett such an interesting character.
That being said, one of the prequelcasting decisions that I happened to agree with was Temuera Morrison as Jango Fett.
Did the voice have to change? Certainly not. Look at Republic Commando, as others have said. Only Boss sounded like Jango Fett.
One can argue that Daniel Logan as Boba Fett already had the Concord Dawn (aka New Zealand) accent. Well, I have a friend who left Australia when he was approximately 10 years old. Now, he sounds like a typical American.
Bottom Line? I don't care either way, I like both voices.
However, I do think Lucas should have preserved pre-SE Star Wars. I think it was a big mistake to try and wipe it away.