Can't access website from same network
After much research, I found this article on the Comcast forums: http://forums.comcast.com/t5/Home-Networking-Router-WiFi/SMCD3G-Can-t-access-web-server-from-LAN-from-Internet-OK/m-p/1754823#M55009
Essentially, certain models of Comcast routers (both home and business class) will experience an "issue" where requests made from inside the network "die" at the router. It has to do with NAT, and it appears that some routers will send the request up to the DNS server to resolve, and some will stop the request right there.
The "solution" is to just use the internal IP address of website... though I am disappointed by this, as it seems silly to me that the router can't resolve itself. But, it is what it is.
Hopefully this answer helps anyone else running in to the same issue as myself... trying to figure out why a site can be accessed externally and not internally.