This is definitely somewhat true for a project like this. It's basically generating an initial batch of sales to fund the production of the product, which is great in my opinion.
What's amazing about this is that this -- funding development through sales -- is incredibly difficult to do for free software projects otherwise. You have to front all the costs and rely on the generosity of donations or recoup the money through support and services.
Edit: And I think the point stands notwithstanding the fact that Light Table won't be free software.
Edit: And I think the point stands notwithstanding the fact that Light Table won't be free software.