When we launched WPtouch Pro, we received backlash at the time from people who were adamant that you couldn't charge for a GPL product. Thankfully we rarely get that anymore. But it's nice to see more discussions around the GPL and business models for WordPress products.

Neither Dale or myself ever had any aspirations with turning WPtouch into a professional version back in the day. But we hit a point, somewhere around the 1.5 million download mark on wp.org, where we simply couldn't keep up with the support requests (often coming to me via my personal website). At the time we were both working full-time jobs in other careers - Dale was doing social work, and I was working in the Voice over IP industry. We would have loved to work less at our day jobs and more on WPtouch, but the donation button we had in the admin panel only yielded about $500 on donations at that point. At that time, 2009, WPtouch was voted the #1 plugin by WordPress users (Matt Mullenweg showed a slide to this effect at WordCamp SFO that year). So even though it was one of the most downloaded and most popular plugins at the time, people just weren't supporting it through donations.

As a result we ended up creating the commercial version with the hope that it would generate enough money for two people to work on it as our full time jobs. We based the original revenue model mostly on the Gravity Forms model (thanks Carl) which seemed to be working for them. I agree though with people who say support wouldn't work as a model - if we didn't charge for the distribution of the code and future updates along with support, I don't think we'd make much money at all. Same goes for documentation.

What many people maybe don't realize is that many premium plugin authors use the funds of their premium products to fund development of free versions. For example, we have three free plugins that we regularly try to update - WPtouch, WordTwit and Piggy. WPtouch undoubtedly helps with sales of WPtouch Pro, but the other two don't have any commercial ties. Without the money received from the Pro version, we wouldn't have the resources to continue work on our free products. And we enjoy using these products ourselves, and are happy to continue working on them since others seem to like them too.

Like many premium plugin and theme authors, we have the trademark for our product 'WPtouch Pro'. So while the GPL protects the freedoms of the person who bought the software with respect to the usage of the code, it doesn't give them the right to resell the product as WPtouch Pro. They can rebrand it and sell it as something else, but they can't sell it as WPtouch Pro. That would be confusing to consumers (similar how going to a website with wordpress in the domain might make someone think it was an official WordPress site), and one of the things that trademarks are meant to protect.

I think for most of our customers though (99% or higher), the intricacies of the GPL aren't relevant - people come to our website looking for a mobile website solution and simply buy it because it looks like it will solve their problem.