People are opposed to learning yet another tool. But here's the really funny thing about the "use a more robust language" argument: not only do they introduce more dependencies, they can introduce more bugs (due to increased complexity), and are almost always a maintenance headache. The one thing that's easy to maintain after 10 years is a shell script. Perl is a nightmare to maintain after 10 years (mostly due to the lack of good Perl programmers) and awk is just barely better.
I did not realize dash was bourne compatible. Also, I'm curious what systems you've used didn't have bash installed by default, as I haven't used anything in a long long time that didn't have bash.
By default I write Bourne, and if I need the extra complexity/speed/etc i'll switch to Bash, but it's pretty rare that I need to use Bashisms.
I don't understand why people are so opposed to bash in general when it's so powerful for how straightforward it is.