It's a pretty popular project management software, 56 employees at this point if I remember correctly, probably millions in revenue. It's a tiny, bootstrapped company, no investors breathing down their necks, no IPOs, nothing. And they're one of the few companies who actually have principles, are committed to privacy etc.
The vast majority of companies like this have perfected the lock-in strategy to ensure that their customers can never leave.
Is that unique to Basecamp or does it apply to all similar software? I haven't Basecamp all that much. What exactly do they do to ensure this?
There's also the idea that if you provide an easy way to exit the service then people are much more likely to buy the service. Since they know they can easily get out of it if they don't like it.