Unix weenies are spoiled - the text-based Unix tools for distributing
sources have been developed over years of source distribution. There
are tools like metaconfig and autoconf to help with portability, and
everybody knows what a Makefile is.
Windows and Macintosh tools are much harder to untangle this way.
I know; The PGP 5.5 source code had grown intertwined with bits
of Eudora, InstallShield, etc. that couldn't legally be published.
Netscape is probably in a worse position, with all the third-party
code they've licensed.
It would be nice, but the value of starting another development branch is
dubious and it does have a significant cost. I think it's probably better
all around to find ways to prune the Communicator 5 code.
-- -Colin