Backstory. This post is a reply to some thoughts expressed by John Gruber in his post “What if Flash Were an Open Standard?”.
First of all KHTML never was under BSD License. It is under LGPL (or other GPL compatible license if I’m wrong about LGPL). So WebKit just couldn’t be closed up as it’s a KHTML derivative. But even putting licensing aside I see other much more important reasons for keeping it open source.
A decade ago Mozilla stepped up to “take back the web”. And it had a lot of troubles doing that just because web was developed for IE. Mozilla seduced developers by standards and new features and eventually (a decade later) it finally took the web back. Note, that Mozilla browsers was cross-platform. They had a broad potential auditory - all windows users, every major alternative platform like Linux, BSD family, OS/2, BeOS, Mac OS. And still, it took some time for web to accept new standards and start coding for two browsers, because Mozilla browsers was not completely compatible with IE. Or for three browsers because there’s Opera too, which has it’s own incompatibilities.
Apple want best experience possible for its customers. And nowadays web is a big part of that experience. So that’s kind of important task for WebKit.
Now, how do you think, what makes developers to develop same thing for one more browser? OK, management does, but what makes management decide to develop same thing for one more browser? It’s not a cheap decision. The answer is popularity of platform.
By the time of first Safari back in 2003 OS X took about 3-4% of all web surfers. So how to convince many companies to accept another browser with it’s own (not numerous but still) incompatibilities? Of course, make your platform more popular. So Apple instead of locking it up made WebKit open source. That instantly attracts attention of developers. First just to tinker on a weekend, then to try it for some serious stuff. Now, as you can see, WebKit is not only Safari. It’s Chrome. It’s a lot of small browsers with a small userbase but it all adds up and now WebKit takes from 10% to 15% of web surfers according to different sources. So WebKit userbase twice as bigger than Mac OS userbase. And now with iPhone and upcoming iPad it’s even bigger. Also as a bonus open source project has some free manpower for development and testing.