Companies are able to thrive by developing and running such "simple" systems because of characteristics of the typical consumer and the reality that even "simpl

Companies are able to thrive by developing and running such "simple" systems because of characteristics of the typical consumer and the reality that even "simple" systems tend to be more complex and difficult to implement/run than they appear from the outside. The typical person lacks the time and skill to install open-source clones of web applications. The typical person does not even have a server on which to install those applications! Running a high-quality, reliable service is difficult. There will always be nitty-gritty pain-in-the-butt performance and reliability issues with anything that gets popular and thus needs to scale. Solving those problems requires compensation of some sort. These factors are what enable companies like 37signals to exist even if/when they are cloned by an open-source project. Then there also is the continued innovation that happens while the clones are busy playing catch-up, and the loyalty happy customers feel towards their craftsmen toolmakers.