Nick, note that there's a population that should find OmniPlan 1.0 ready to roll out of the box — that crowd at WWDC. Small groups, building iPad apps, everyone on the team has an iPad, probably not report generating fiends, in other words, Omni built an app they would find useful in house. It seems like a pretty obvious stepping stone on the way to a more widely useful app, allowing them to grab some mind and market share, get some useful feedback and direction, etc. If you aren't in that target population, and can't imagine that an app might rationally be (initially) targeted at a group that doesn't include you, then sure, it might look like a mistake.
But that's not what professional project management means to me, and I've seen what Omni have invested in OP/Mac to make it serve something much more like my view of PM than what you've described - especially the work to coexist with Microsoft Project, the standard many of us have to work with.