The colon is there to make it easier on editors that want to do auto-indentation. Their logic can simply be that if the previous line ends with a colon, then add a new indentation level.
Now we supposed to help editors? ;)
I thought it should be otherwise... editors supposed to be helping programmers.
Programmers can learn syntax. Regular humans can't. Both Python and Ruby failed to provide a simple way of building internal DSLs. In Python humans need to be specific about indentation and ":" and in Ruby they need to remember all these stupid sigils.
