chmod +x is necessary any time Linux programs are distributed in .zip files. Zip doesn't save any of the system flags that Linux uses to determine if something's a usable program, so the system assumes it's not unless it tell you.
This could be fixed if the program were re-compressed into a .tar.gz archive instead of a zip archive, but it'd have to be done on a Linux [or Mac I guess?] computer because Windows doesn't track those tags either (so they would still not exist). It's not really a big deal, but it might be good if DU&I mentioned it in the readme.
Sorry for long response you didn't really ask for, I just thought this might be useful information for someone.