Any effect is google ranking, if site link is as: http://www.sitename.com/ and blog is as http://www.sitename.com/blog Root dir files and sub dir files can get same pr?
Yes, Sub Directories can get the same PR as root directory. Sub directories are anyways part of root directory & it makes it much easier to keep things compartmentalized and reduces the chances of accidentally overwriting some important file. It will also helpful to keep your root directory clean. It will be easy to manage a folder rather than messing it up with the other root files. but don’t be too much deeper up to too many levels like /dir1/dir2/dir3/dir4/page.html, because search engines can overlook these pages.