It's fun to contrast this with Lua, by the way.
In Python, you can make anything callable by providing a __call__() method, and the parentheses will work as expected. This makes functions fungible with anything, including any object or anonymous function.
In Ruby, only methods are callable, and everything else must be called with the call() method, which means you can't use one in a place where the other might be expected. They're two concepts with the same verb--call--that require different syntax. It's inconsistent.
In that sense, I see why it's not so bad; the difference between methods and anonymous functions is very explicit, and when you want to pass things around, it's likely that you will have target code which expects a Proc object and source code that generates it. Perhaps it's not so bad because there are few legitimate use cases, if any, for transporting a method when an arbitrary block is expected.
As wycats pointed out in a post earlier this year (http://yehudakatz.com/2010/02/21/ruby-is-not-a-callable-orie...), the reason you don't need to explicitly call #call on methods is that Ruby is designed for the common case of calling methods. In addition, it's uncommon to even explicitly use #call or #[] on Procs since calling them is built into the language via yield.
