Here’s a quickie for you. The other day I scraped all the themes from WordPress.org (615 in total, or at least that’s what my script pulled down) and then plotted how complex the theme was based on when it was created.
I used two ways to measure complexity: how many files were in the theme package and how many bytes were in the non-image files inside the theme package. These two metrics are somewhat related (we would expect the number of bytes to increase as the number of files increases) but also tell slightly different stories.
Number of files in a WordPress theme over time
Number of bytes in non-image theme files over time
Not counting bytes in image files is important because we should expect the quality (and thus file size) of images to increase over time.
Writing a theme is getting harder over time, and I suspect that this could be said of web sites in general. We need to work to make sure the tools for web authoring improve at the same rate as the level of sophistication expected by web authors and surfers.