I've just compiled p7zip (opensource *NIX command-line 7zip port) on my Linux box and successfully un7zipped my installer. So pretty much both Windows and *NIX folks are safe with this distribution method: if they cannot run installer they can manually unpack it just like typical archive, every tool is free and opensource. Good for a long-time run.
As for DOS extracting I'm not sure. But even if there isn't way for pure DOS how're you supposed to get this file anyway? Don't tell me about browsing web in DOS... Sounds horrible... :-)
p.s. yea yea, I know... sitting under root in linux is baaaad, I don't usually do that, I'm just lazy sometimes :-)