Ditto.
Another good example is Cappuccino/Objective-J. One of my favorite things about the whole Cappuccino/Objective-J framework was that 280 North built 280 Slides with it very early on. Going through the paces of developing an actual app with your framework is an essential process to creating something really useful.
The fact they've already decided they're not going to actually build a sellable product on top of it anytime soon is worrying, to say the least.