Well, not everyone bothers to read the full description before making their decision, but the App Store description for OmniGraffle for iPad does clearly state that you have 30 days to ask for all of your money back if you don't like it, and I see no reason to believe that Omni will not include OmniFocus in that policy (http://www.omnigroup.com/blog/entry/30_day_guarantee/).
No doubt there will be people who don't even look at the app when they see the price (whatever it is), but below some price point, for an application you want to support and have your customers actually use for more than a few hours before tossing it aside, it just isn't worth the trouble to get most of those people on board as customers. Disposable app <-> disposable customers. Figuring out just where that limit is is something I'm glad I don't have to do :)
No doubt there will be people who don't even look at the app when they see the price (whatever it is), but below some price point, for an application you want to support and have your customers actually use for more than a few hours before tossing it aside, it just isn't worth the trouble to get most of those people on board as customers. Disposable app <-> disposable customers. Figuring out just where that limit is is something I'm glad I don't have to do :)