However, thanks to a Tweet-tip from Steven Troughton-Smith (@stroughtonsmith), there is a way to enable this functionality. To add Multi-Touch maps to places in iPhoto '09, just open Terminal.app (/Applications/Utilities) and type (or copy/paste) the following statement and press enter:
defaults write com.apple.iphoto MapScrollWheel -bool YES
When you restart iPhoto, you will notice that you are now able to scroll in/out of the Places maps with ease. If it turns out that you don't want the scrolling feature, just retype the statement, replacing "YES" with "NO."
Thanks for the tip, Steven!