Thinking about the ubiquitous confusion surrounding the concept of 'free'; yes, Linux is 'free' and yet it is a 38 million dollar industry, so somebody is paying for something. I think the proper analogy is this: Linux is to programming as ...the English alphabet is to anybody who writes in English. To use it properly and effectively you still have to know the basics of grammar and not just anybody can write Moby Dick.

If you stretch the analogy further, programming code, whether Linux or php is like all alphabets, meaning that code is as old as Cuneiform tablets, and so is the concept of free. This brings me to two other commonly confused points regarding the concept of 'free': free as in free speech and free, as in free beer. They are not the same, i.e. your right to free beer is not guaranteed in the Constitution.