alt Hacker NewsNo, they are not.
The Debian/Ubuntu family uses the "Debian Almquist Shell" (dash) as the system shell (#!/bin/sh) for a number of reasons. It is very much not compatible with anything fancy from bash (or korn). The bash shell is available as #!/bin/bash, but that opens the door to a new set of problems (in that POSIX mode is not enabled).
In the embedded realm, busybox also implements the Almquist shell, but it does throw simple bash "slang" back in (but not this does not include arrays).
How often don't you have bash on a debian/ubuntu system though? #!/bin/bash and away you go. Every workplace I've been that uses debian just goes for bash in the shebang.