Can someone explain what an ASA can and can't route?

Inherited environment with an 1805 and an ASA5510. There are a bunch of static routes on the 1805 but it's not doing any dynamic routing. The 1805 is the default gateway, the ASA handles firewall, DMZ and VPN.

Can I put the routes on the ASA and get rid of the 1805 (after making the ASA the default gateway)? Any idea why would it have been set up this way? The router does not have any public IPs, but the ASA does. All the static routes are like:

ip route 209.x.x.0 255.255.255.0 172.16.x.x

There is traffic shaping set up on the 1805, but I am guessing that isn't relevant here.

If this is covered somewhere in an article, please point me in that direction.

Thanks bigtime