Convenient, central app admin.
Can use iTunes gift cards.
Subscription pricing - with access to many more top tier apps included.
A few other points worth considering:
- Functionality-wise, the apps are identical
- All apps support iCloud 'syncing'.
- Purchasing direct from this website is safe, secure and handled by Fastspring.com (as used by Adobe, Smith Micro and Smile-TextExpander amongst others.)
- Updates to the app are handled automatically regardless of the way it is purchased.
- All license schemes allow the app to be installed on multiple computers (so long as only one person is using it at any one time.)