First, he says he would never sell the company, not for 150 million dollars, because he's not in it for the money. So, ok, he won't sell the company.
However, he also said, you should always be working on your best idea. If you're not working on your best idea, then you're doing it wrong.
He says that 37 signals and its products are his best ideas.
Ok, following me? If one day, he came up with some idea out of the blue, out of inspiration, out of some life-changing event, out of...wherever.... and that turned out to be a better idea than 37 signals....ummmm then what?
Then he should sell his company to go work on that "best idea". No?
2. he addressed that - at least this idea works for them right now and had for past 10 years
3. starting from scratch now will not yield answer to whether new idea was better in next 10 years
You wouldn't exactly have a 37 signals homepage that showcases Basecamp, Highrise, Backpack, Campfire, and now introducing World Feed, the solution to World Hunger!