There are several reasons why we might need the flexibility of bash over a Linux dist format like RPMs or Debs, like being able to support different architectures (FreeBSD, OS X). We would need to pass a large number of parameters to the install process, which could be through a single, global and well commented config file. Then there are source modifications (OpenFTS doesn't even compile 'out-of-the-box' on FreeBSD), PG tuning (BLCKSZ, shared memory segment size, kernel limits, --enable-locale --enable-multibyte), format and location of startup scripts etc. Loads of fun!
The current install docs are somewhat Linux centric, and a UNIX newcomer would face a few rough spots if trying to install OpenACS on, say, FreeBSD by following them. Personally I have adopted the habit of keeping a large file of shell command snippets around, for when I want to repeat a particular operation again, but a set of well tuned install scripts would certainly be welcome.
If someone champions the project and shows how it should be done, then I would like to help by modifying, testing and maintaining the FreeBSD/PG parts of the install system, if multiple architechtures will be supported. Note that an architecture may also be a Linux distro, like redhat or debian.