It doesn't help matters at all that bash leaks bashism-support when run as /bin/sh -- it's much better that people specify bash than ship scripts that falsely claim to be bourne-compatible (since they are unlikely to test against a pure-bourne shell).

Not having a /bin/bash a losing battle -- it's way too late to get people to use the theoretically more correct #!/usr/bin/env bash just because the greybeard unices don't ship with it (despite shipping with plenty of other GPL software) and their package managers put it (when they are nice) in /usr/local/bin

Edit: That's not a diss on the greybeard unices -- I used FreeBSD and loved it dearly for years. I actually really like that they segregate all user-installed packages into a seperate root at /usr/local/ -- but for practical reasons I always make symlinks for binaries with well known locations (to use the robots.txt / favicon.ico pejorative).