Designing a character class in Diablo III is a different experience from doing the same in Diablo II. You're no longer restricted to earning a skill point to spend on a skill tree every level—an action which carried the hazard of spending said skill point on the wrong skill.
Instead of skill points, characters will earn skills and skill modifiers (runes) at predesignated levels. You may be a little taken aback by this development, but this new system allows Blizzard to put a greater emphasis on itemization and frees players up from following cookie cutter character builds.
Essentially, you can play the game as you like and alter your character as you acquire new items, or switch skills to deal with different challenges as you progress through the world.
Responding to an irate fan on the game's official forums, Diablo III spokesperson Micah Whipple had the following to share:
"So, a couple things, Diablo for a lot of people is about non-optimal builds. It’s about finding some crazy-!@# build that no one thinks should logically work, and using your knowledge and skill of the game to defy logic and make it successful. So just switching skills between direct parities is probably not going to be a monumental discovery that will win you an award in character building. But, that’s not where the real fun and challenge of character builds generally come in. It might be fun for you though because one skill is purple and one is yellow and you really love purple, and if that makes the game awesome, awesome. As you said there are plenty of bad choices to make, which means there are plenty of non-optimal – but still potentially viable – builds to attempt.
The issue that you’re taking though is actually one of customization. What you’re saying is that by having these close parities between skills there’s less choice, and in fact the exact opposite is true. If there are sharp distinctions (as you argue is superior) then there are sharp separations, and sharp separations means that very clear correct choices emerge. By having more parity it allows for more customization as it allows players greater freedom in choosing the skills they want to use, and not the skills they have to use because the math makes it so. Again though I’d argue that there’s plenty of gray area in character builds, and that’s where the true excitement and discovery comes from.