I applaud the fact that a developer can charge for his time and effort into building a good product. While I love hearing about these success stories, lets not forget the fact that all applications are different. There is an inherit and perceived value for everything and it's all dependent on the audience. The ROI per user is different for everyone, what works for you may not work for someone else. Marco's audience is made up of mostly tech savvy individuals where the implied value is greater than the cost of the service. This isn't the exception to the rule but it isn't the typical audience that a lot of startups are trying to capture. Every audience and product is different and take inspiration with a grain of salt. With that being said nice work Marco.