Isn't selling open source extensions illegal, or at least immoral?
This is a common misconception. Many Free Open Source Software (FOSS) projects are 'no cost' to download. But this doesn't mean they have to be. The 'Free' in FOSS refers to freedom, and not to price. Just read the third paragraph of the GPL License which is the most commonly used FOSS license in the world.
We also feel that there is nothing immoral about desiring a fair compensation for our efforts. We all have families to feed, clothe, take to the doctor and provide for, and we can't subsist on goodwill and download counts alone.Our prices, taking into account our level of support, and the number and quality of our extensions, are the best in the world for any commercial CMS company.