This website is on Drupal, but amongst other sites that i manage, is one that has been running for over 10 years on Wordpress.
At the time I set it up, there was a vibrant community producing free (as in speech and as in beer) opensource themes and plugins.
I took one of these themes and modified aspects of it to suit my own site while crediting the original author (sub-themes weren't something that existed at that time).
Now, I am looking at upgrading the theme, to something that takes advantage of all the things that have happened in the intervening time - HTML 5 compliance, fully responsive across different devices etc. I'm dismayed by the state of Wordpress themes today though - the unverse in which they exist seems completely different to the one I remember. If you search for Wordpress Themes, almost every site just lists large numers of paid for "premium" themes. Wherever you think you have found an open source theme that does seem irght for your site, you discover that it is merely a "lite" version - its main aim being to upsell you to the premium version that adds additional features.
Now - if you want a fully customised theme for your site without putting any work into it,then the premium options might be a good choice - yet, it seems that the original ecosystem of opensource themes that Wordpress built its reputation on has withered away to nothing. Other than the standard ones included in Wordpress, if I look at the most popular ones on Wordpress's own site, all either want me to pay for them, or have a premium version.
Various websites extoll the virtues of premuim over free - the extra features, technical support etc. But nobody has explained why these can not be available in free themes. It can't be about the complexity - afterall, Wordpress itself is free and opensource, as are many far more complex projects. Maybe the high quality free themes are out there, but they are definitely not easy to find.
As a contrast, Drupal seems to have perhaps stayed closer to its opensource roots in this regard - the popular themes on Drupal's website all seem to be free, and there are various free frameworks for developing your own themes from, such as Omega and Zen. WHy Drupal should gone in one direction and Wordpress in another is unclear - but what has happend does entirely alter people's perception /understanding of opensource software.