Just because it's business doesn't mean it's not altruistic. pg does YC because he wants young hackers to do interesting work and solve the money problem, but he wants a return. Joel wants people to manage their time and get their work done in an organized way, and he believes in that so much that he wrote a product that does it. I'm sure he wouldn't care if you used any great product to track your time, but there's only one he can offer for free.