First of all, within free software, collaboration is a lot easier than competition. Sure, we should all try to be the best we can be, but if our "competition" is also free, we can just grab their stuff and re-use it. We cannot, however, grab whatever we want from Matlab and re-use it, so we do have to compete against them.
Secondly, even if I agree with you that competition is great even in this case, how do you want me to modify my behaviour? To stop collaborating with Julia? To view them with more suspicion? To refuse to help them when they ask for help?
I already try to match features whenever possible. The feature I'm most envious of is their JIT compiling, but it's very difficult to implement this. Vice versa, I don't think they have a goal to match our features, such as a native Qt GUI or an exact implementation of the Matlab language.
Julia and Octave have lots of ideological differences too. For one, Octave is a GNU package, so it tries to adhere to the GNU coding standards and ideals. In particular, we prefer to call ourselves free software, not open source, even if both terms mean the same thing. I think the most important thing is to enable unfettered scientific computing. Julia's main goal is to provide a better language for scientific computing, while ensuring user freedom is a secondary goal. So far they have not compromised user freedom, and I hope they never do. So, there you have it, we're already competing on something?