For me, the question isn't so much what Ruby has that Python lacks, but the extra Python bits I find annoying and/or tedious:

* having to declare "self" in every method argument — reading code, it just clutters up the screen/page

* the big use of of double underscores for special methods (i.e., __init__, __str__, __getattr__, etc...) — IMV, it's gooberish...

* no switch/case statement

In defense of Python over Ruby:

* I prefer the whitespace over the Pascal-ish begin/end, especially for real life code solutions

* the Ruby shorthand syntax IMV at times obfuscates code clarity - is it a method or variable I am looking at?

That said, I'd much rather code in either Ruby or Python than in Java or C...