I'm not sure I understand the avoidance of CSS frameworks. I'm currently using Mystile theme from WooThemes and it's pretty good, one of their few free and responsive themes. But I miss Foundation Framework. When I try to change the header and footer, quickly the layout falls apart. It's very hard to change a responsive theme that is not based on a framework. You may be searching far and wide to find the CSS applicable to an area of the site, and to understand the logic behind the responsive features is nearly impossible. Personally I'd always prefer either Foundation or another responsive framework as it would make swapping areas much easier. Yes I can imagine if you make a theme dependent on a framework then only developers familiar with it will want to buy it. Yet I'd rather make a product easy to use by a few, then a product that is difficult to use for everyone or that has a sharp learning curve. Perhaps the question is how often do buyers of themes either create a child theme or want to change the layout of the main areas?