Apophysis is merely a tool, albeit a free and easy to use tool, but still it is just a tool.  UF, XD, Chaoscope, Chaos Pro, FE, Fractint, etc. are just tools.  Some are old and significantly out of date and some are new and pushing the state-of-the-art with fractals.  Some are free, and some cost money.  Some are easy to use, and some are difficult to use.  You use the one, or multiple ones, to best express what you are trying to create.

Apophysis is popular right now because it is a very easy way to create images, particularly flame images.  It even generates a 100 or so for you when it starts up.  You don't have to spend weeks or months experimenting and learning the best formula, coloring, and transform options to create nice images.  You don't have to spend weeks or months learning how to navigate the UI to get the most out of the program.  IOW, you have an easy to use program, but quite limited, control over your images.  I think Toby said much the same thing above.

Is there going to be the same discussion when something comes out that supplants Apophysis in popularity?  There will be.  Will there be the same discussion when something comes out that surpasses UF in capabilities?  It is likely at some point there will be.  Will the same discussion take place when something comes out that combines the capabilities of UF, Apophysis, and other programs?  Again, all it takes is a motivated individual or a group of them to pool their talents and be creative.  This is no different than the creative energies that individuals need to use with their particular favorite set of tools to create their art.

In short, isn't worrying about the popularity of a particular program and/or the quantity of images produced by a particular program kind of pointless?

Ken...