I recently tried to update my FCP X from 10.0.0 to 10.0.1.  I opened the App Store to find those updates.  Since I had Compressor 4 and Motion 5 the updates were included and was available to download.  But FCP X was not.  After digging around the app store I saw in Purchaces that Final Cut Pro X was availabe to install.  So I did the logical thing and clicke install.  Logically the App store warned me with the usual warning sign, You have already downloaded this program.  So I simply deleted the old Final Cut Pro X and went back to the App Store and clicked download one more time.  To my delight, FCP X 10.0.1 was begining to download.

All is well!