My iPhoto 9.1 wouldn't update, even after I put it back in /Applications.
But the Apple Support download - http://support.apple.com/downloads/DL1608/en_US/iPhoto9.4.2Update.dmg worked for me too. I added an 's' to the http to secure my downloads against MITM attack
I'm guessing that the final URLs won't work for anyone but me, but here the are as examples:
Unfortunately, the update I downloaded is not willing to update the stripped, monolingual version of iPhoto 9.1 that I had symlinked to. But I replaced the symlink with a copy of the actual (but still stripped and compressed) version of iPhoto 9.1 and the it agreed to install the latest iPhoto.
I'm now running the latest iPhoto.