OK, time for explanations!
There are four reasons why ROX-Filer is not included:
1) Everybody loves choice and freedom - the distribution should include a sufficient file manager (well, since you can't do anything without a proper file manager, unless you're a true Linux haxx0r) that is enough for basic tasks, but always have the door open for alternatives.
2) ROX-Filer is so deeply integrated into Puppy - the only way to cut those ties is to remove it. I'm talking about things like desktop icons - you can't build a Puppy without ROX-Filer unless you modify all scripts that use it, replace /usr/bin/rox (what I did in 5.0.0) or provide another file manager with a placeholder at /usr/bin/rox (what we have in 5.0.1).
3) Two-pane file managers are more RAM-efficient. ROX-Filer requires two instances windows to copy, move or link files. This means, more memory usage and the need to move two windows around the screen.
4) It's good to be special.
EDIT: just to let you know, guys - I already mentioned this in the Exprimo thread - I'm currently writing build scripts for many of Puppy's traditional packages that were included since the 1.x and 2.x days. The reason for this is the fact it's impossible to build a pure 64-bit Puppy without those and porting it to ARM or whatever is impossible.
So far, I have a nice number of packages ready. I haven't tested them yet, though.
The dual-kernel experiment got messed up, something is wrong in the kernel sources. I think it's some incompatibility between dpup's GCC and Linux 2.6.32.x, I'll investigate this once I'm done here.
EDIT 2: more good news - I was able to build the latest Binutils and GCC. Now I want to experiment with eglibc and uClibc - maybe we could benefit from those