Just a word, that dual wan routers often provide policy routing so that you can force packets from or to IPs, or services, or even quality of traffic (TV is 3 I believe) to specific WANS and/or associated VLANs.
The question becomes though if it is best for a single router to handle both internet and tv routing and associated packet handling. If both are being utilized it may be advantageous to off load some of it.
For instance on Bell FibreOp, the provided actiontech router connected to the ONT does a poor job of combined ops. Some here in the Maritimes have replaced it with a workhorse Asus rt n56U router which has throughputs up and down in the order of 800Mbps, a hardware nat engine and a built in gigabit switch that recognized and routes in hardware 802.1p (IPTV) and 802.1q vlans, and TV performance is much improved, very snappy.
This router can also, with configured firmware, bridge to another router on a specific port wrt to the internet traffic.
So at this point a dual wan router can come into play and your home network can be behind this dual wan device. It can use the bridged (Bell wan) as one input and your cable connection as the other input, not worrying Tabout TV or other services etc.....--
Ain't nuthin but the blues! "Albert Collins".
Leave your troubles at the door! "Pepe Peregil" De Sevilla. Just Don't Wifi without WPA, "Yul Brenner"