[lug] stupid router question

[Bear Giles]

This is a really stupid router question, but I want to make
sure that I'm not making an unwarranted assumption, etc.

When I put a box into a colocated facility, a box with a 
competent OS (Linux, *BSD, etc.), why do I need a router?
Maybe I'm showing my academic bias, but I thought "router"
was the box where I have my network on one port, AT&T on a
second and Sprint on a third and this box knew which outbound
packets to put onto the AT&T wire and which to put on the
Sprint wire.

But in a colocation facility, that's handled by the hosting
company - I have a single wire to the rest of the world.  So
the "router" is just acting as a bridge - I should be able to
use a cheap hub instead.

I know that routers also usually include firewall rules, but
that can be handled at the host level with packet filtering
rules.  In an office with plenty of room and lots of dump
OSes, setting up an old PC to handle the packet filtering
makes sense.  But in a colocation facility space is expensive
and I would prefer to avoid having to find and set up a used
router if a cheap hup and some IP/PF rules would suffice.
So is a router really necessary?

Bear