Saw this on reddit a few days ago. You could make a lot more money with it by making it a hosted solution and charging monthly/yearly.
The fact that it can be purchased and installed is the differentiating factor and may target a market audience that's largely ignored.
While there is usually the potential for higher sales with a SaaS approach, that doesn't mean it's always the correct fit when entering a market.
You could undercut Basecamp by a sizeable margin and still turn a nice profit.
Of course, as mentioned above, saving time not having to support customer installations could (easily?) offset hosting costs.