I'm not 100% sure, but I believe that since the retail version of Lion on the Mac App Store is the same build (11A511) as the Gold Master released to developers, you will automatically receive the updates. You're essentially running the retail copy if you installed the Gold Master.As for GM build etc. - I get the following message when I click the "Buy" button - "Install Mac OS X lion 1.0.4 is already installed and was not purchased from the Mac App Store. Do you want to buy OS X Lion 10.7?"
Wonder if this will mean I don't get to update when updates come out.
Since the installer that you used to install the GM is the exact same version (1.0.4) as the installer that you would purchase from the Mac App Store, it recognizes that you're buying the exact same thing again. You would pay $30 on top of your already-free copy. (Free excluding the annual developer fee.)