To developers: If Android is an official target in Nokia's Qt SDK (or whatever it's called) then developers can target Symbian, MeeGo and Android at the same time.
To customers: Nokia can guarantee that their customers' favorite apps are published on 3 major platforms (symbian, meego and android). So the customers will not need to worry so much about OS selection, as long as they stick with Ovi/Nokia.
All this will increase long term value to Nokia's platforms, serves as bargaining chip against Android.