I think a surprising number of people probably just use an ISP-provided modem / router combo, allowing the ISP to set the LAN's DNS, decide how to hand out IPs through DHCP, and other configuration options that give them way too much control. A shrinking number of geeks use their own router, and a tiny fraction of that shrinking number even uses their own WAN interface.
Many of the posters here seem to be missing the point. 99.9% of customers using ISP supplied equipment don't care about internal DNS resolution, grandma just wants the internet to work and most consumer grade peripherals like printers just use zeroconf anyway, bypassing DNS completely.
