Most cable companies do not. DSL often gives you an all-in-one-POS (and charge you a monthly rental fee). It's a question of how far their service should go. In my opinion, their job is to get the Internet to my house. After that I'll do what I want with it. Other people want a more complete solution. How far do you want them to go? Provide a modem? Provide a router? Provide cabling throughout your house? Provide the computers you use to access the Internet?
I have dsl from centurylink. Our shitty zyxel modem they gave us only has 1 ethernet port and is slow as tits, but when i install my new modem, my connection constantly gets booted for pulling too much bandwidth. Youd think that a big isp like centurylink would know to throttle connections rather than booting them.
Also, most routers nowadays will allow you to clone a MAC address. So, if you know the MAC addy of your ISP's router (probably on the bottom of it) you can "spoof" or copy that set of numbers to your new router and your ISP won't know shit. They'll see their equipments MAC and think nothings wrong. -Alternately- You could just do like everyone says and use a router after your ISP's router or modem. They'll just see one connection and be happy. Good luck!
If you have a 20 -40Mb connection, buy their $99, Q1000. I have a friend with CenturyLink and his returns are near the max 40Mb. The nearest competing modem is about $149.