For common sense
First, when you dial your own Google Voice number, we now begin playing your voicemails without the need to press 1 anymore. Since listening to voicemail is the most common reason people call their own numbers, we thought it made sense to save you an extra step.
And you really begin to wonder why it never made much sense to carriers earlier. They require a heck of a lot of key presses from me before I can get to my voicemail.