Olivia's audience is also about half the age of Arthur's. Arthur has the reputation of being a preschoolish show, when it's really more aimed at the 2nd grade set, which is a world of difference.
Olivia isn't going to change the world of prechool animation, but it's the best animated show on Nick Jr. in years. I personally find it very well written, imaginative, well animated, and relatable to it's main demographic while still being entertaining for everyone else. I like the calm, easygoing tone to the show too. It reminds me a bit of Little Bear meets Little Bill at times.
I'm pleseantly surprised that the show got this kind of props, I didn't think anyone was watching it.