The Database Update functionality is broken for Mac 10.6 users due to us upgrading our Xcode compiler -- please accept my sincerest apologies. Apparently there are now some new flags to enable 10.6 support which we had missed (Apple sure makes you jump through hoops to support older versions of their stuff). We have submitted a patch to Apple, but in the meanwhile, for those who want Magic 2013 immediately can follow these steps:
1) Copy the attached file to your Downloads folder. For those using Safari, right-click the file and select "Save Linked File to Downloads".
2) Start Terminal (Command-Space, then type Terminal)
3) Copy and paste the following command into the Terminal window, then execute it
cp ~/Downloads/DBUpdateDatabaseWindow.nib "/Applications/Decked Builder.app/Contents/Resources/DBUpdateDatabaseWindow.nib"
Should it complain about not having permissions, you might need to prepend sudo to the command.
Hope that helps! You should be getting a patch 2.7.7 from Apple (already submitted) hopefully within the next two weeks.
- Tan Thor Jen
Edit: Screenshot attached below of the wait for Apple's approval.