You can blame me. :) I started filling out the various sub-directory READMEs as I thought putting too much information into the single INSTALL.txt might be overkill, hence the:
"Note: Because of license restrictions, Pd cannot distribute the ASIO SDK source
files. If you want to build Pd with ASIO support, see asio/README.txt for
further instructions."
Maybe that info could be elaborated/highlighted more?
Also, changing the directory name was more for future proofing and possibly avoiding broken builds if/when they update ASIO, although that may not really be happening any time soon.