What you keep ignoring is that highcharts is way better than those alternatives, and that many people really like the simplicity of paying people for great products.
That may have been true 4-6 years ago. In 2014, that's no longer true.
That's one of those "It depends" situations. I've reviewed most of the charting libraries that have been posted in this thread and although yes they have come an extremely long way from 4 years ago when we picked Highcharts; all of them would still need a lot of work from our end to add extensions to be able to build all the charts we have in our products using built-in Highcharts options. But like I said it depends, a startup might not want to pay that money but that $3000 for 5 dev Highstock license is way less than the salaries needed for 5 devs to write the custom extensions in order to use something else to meet our needs.
Not sure which part isn't true in 2014 - that highcharts is way better than the competitors or that some people like the simplicity of paying money for things? For me, the first is less true than it was 4-6 years ago but still true and the second is more true than it was 4-6 years ago.