Yes, even though the game is basically the same they're different things meant to provide different experiences.
URU CC is strictly a lonely single player experience, which considering that one of the key points in URU is to understand the D'ni fall and witness its result in URU and in the Ages feels very much like the right place to start, while MOULA is more oriented to online interaction with other folks even if the content available is roughly the same in both cases. There are however some diferences in terms of content, like the items scattered around in both versions and some other nuances.
Personally i think the right way to go about it is to play URU CC first, for the 'lonelyness' aspect i mentioned above and because if you decide to move to MOULA after that you'll have already learned alot of stuff on your own, instead of having to rely on other folks to explain most stuff to you.
After URU CC you'd have two choices, either move to MOULA or if you're not interested in online gameplay with others but still want to see some of the differences in terms of content in MOULA you can always import MOULA's Ages to your URU CC install using drizzle.
Having said that, the Myst/URU community from what i've seen and by all accounts seem to be a bunch of really nice folks, so if you're the kind of gamer who likes online gameplay with nice people i'm sure you won't be dissapointed if you go straight to MOULA.