It is a convention that when you say "written in bash" it means "using bash language and standard *nix binaries". Bash alone can't do anything, nearly every keyword in it is actually a binary, including "echo", "true" and "false" or "[" used in if statements, which you can usually find in /bin or /usr/bin. You couln't write simplest bash scripts without using any binaries.
Netcat (nc) is built in to nearly every system that has bash. Wget and Curl on the other hand, are not.
echo, true, false and [ are builtins in bash and are in the binary. You can even do TCP/UDP through bash by using the pretend redirect files /dev/(tcp|udp)/$host/$port.
curl or wget exists on most systems by default in a minimal installation now days, nc does not, but if you run a normal installation you will get it though.
It looks like it'd work fine without them, it just uses them if they're available (presumably they're more efficient/reliable than using straight bash)
I was just thinking about this the other day and wondering if anyone had tried it yet. Too lazy to look for it.
Throw a way to do some real routing in there and you might be on to something. It's an interesting idea, with the trends of blogs (like mine even) going to octopress, simplifying the serving of static text is greatly beneficial.
EDIT: I think this is it: http://ur1.ca/f2ozi