It is my understanding that the extention doesn’t matter (at least not any of the common ones ie html, htm, php etc.) but that putting them in a folder does hurt the results. I do not fully understand why, or truely know if this is so.
My theory as to why this may be true, if it is true: I could see g00gle considering something in a folder less important, or less related to the main topic of the website.
I am no SEO expert (I ran my site for years without knowing what SEO meant, I used word of mouth in the real world to get sign ups) I am interested to see other points of view!