I totally agree, buying themes is a crap shoot (mostly crap). But there unstated problem with the standards based themes is they are BORING. It sounds so wonderful that you could change themes easily, but in my experience changing a theme is the last thing you want to do - you do it if you are forced to with a gun to your head! I publish a thousand wordpress sites, and I am standardized on about 20 themes that seem to work (fingers crossed).