The first iPhone had 8GB. The Watch has 8GB of onboard memory. Although right now we can't get access to it all. In time as apps become more independent of the iPhone. Will the iPhone have more than 8GB?
I think since it is meant to piggyback off of the iPhone no. Now that being said, maybe in the future if they go more of a standalone product route with the watch then yes.
I think for now Apple as well as users would rather battery life. The race will be how long until the watch is more independent of the phone.