What is the GPL?
GPL stands for GNU Public License, a license written by the Free Software Foundation. The GNU Public License gives you the freedom to take any piece of GPL-licensed work, change it, and release it for yourself, either for personal, public or commercial use. It's one of the guiding principles of WordPress and something we believe strongly in ourselves.
I got started in open source by using -- and later designing for -- an open-source project called Ampache. It was my first real direct involvement in open source (outside of being an occasional Linux user). If it weren't for the GPL, I may never have learned about PHP, CSS techniques, MySQL -- in short, I may never have chosen design as my future path in life and art. Software that is not released under the GNU Public License restricts curious and capable individuals from poking around in the guts of things, which can often lead to better software, faster updates, more security patches and more community involvement.
What the GPL does not guarantee is any kind of warrantee or support. Think about it: if a software developer puts their (presumably working) software out there, and you make changes that break either the software itself or your computer/webhost/server/whatever in the process, it's not the developer's fault that you messed it up. For that matter, any developer is really only limited to his or her own development environment -- there are a million variables for user experience based on the type of machine you run the software on, what your personal settings are, the operating system you use, etc. Without an unlimited (or at least, a very large) budget, it's not possible to account for all of those variables, and therefore no warrantee is included in the GPL. Even companies with huge budgets (like Adobe or Microsoft) aren't able to release products that are completely bug-free.
By purchasing a Museum Theme, however, you are entitled to support via our support forums and lifetime upgrades. We'd be naive to assume that there will never be any copies of our themes out in the wild that did not go through our checkout process. But those copies do not come with support or upgrades. We spent a lot of time designing and developing Museum Themes. As much, if not more than we spend designing and developing for individuals and businesses. By purchasing a Museum Theme, you get the fruits of our labor at a fraction of the cost and the ability to make any additional modifications as you so see fit.
Free software does not mean software shouldn't cost anything. Free software means that individuals should be free to explore, modify, customize or otherwise use said software however they choose. That may mean unzipping a WordPress theme and uploading it to your site, or that may mean rewriting the source code of the core WordPress software. It's not for any person or organization to say what you do with your software. WordPress was released under the GPL to ensure that both it -- and any- and everything that comes out of it (plugins, themes, variations like WordPress Mu, BuddyPress, bbPress, etc) -- is, and always remains, your software.
We believe in freedom. We believe in open source. We believe in your inherent right to break things. We believe in your right to put them back together again in a new form. To learn more about your rights under the GNU Public License, read the full license text, or visit GNU.org.