True, but they aren't readily apparent to someone who isn't digging through the weeds of both languages.

I looked at 'Hello world!' and FizzBuzz written in both Python and Ruby, and thought that the implementations looked fairly comparable. I haven't seen enough to convince me that Ruby is vastly different - not to say that it won't happen, but I haven't experienced it yet. I think that's why the gut reaction is to think of Ruby and Python as parallel languages.

The comparison seems natural to me. They're both targeting the "trade performance for developer productivity" niche. Regardless of how different they might be in execution, their intended purposes have much more in common with each other than with C, Java, Fortran, or Haskell, to name a few.