Basically, one website = one standard license. So, however you would define a separate website in terms of what you’re setting up, would warrant a separate standard license. With an extended license, there are no limits in this regard.
This is a good page on ThemeForest that outlines all of this: http://themeforest.net/licenses/
In my opinion, if a client has a website + blog that both make up one website, but with two separate WordPress installations (for whatever reason), I would consider that all one website, and thus I’d say you’d only need one standard license.