DVB-T tuners are pretty cheap because they're highly integrated and mass produced in huge numbers - you can get USB receiver dongles for under $10 in single quantities. There are even SoCs that integrate a processor and DVB-T demodulator on a single chip, usually used for stuff like set-top boxes.
Yeah, several companies make them, they're very popular in cheap set-top boxes. Having found what I think is the Broadcom press release you're referring to[1], the thing that's unique about their SoC is that it supports DVB-T2 which is newer and less widely used or supported. Looks like ALi have just announced a SoC for that too[2], though unlike Broadcom's it requires a seperate tuner chip.
Oops, I read your first comment as saying "CPU, demodulator, AND tuner". Yes, there are lots of chips that integrate a CPU and demodulator, including the ultra-popular RTL2832U, very popular among SDR hobbyist (as combined with E4000 and other tuners).
