I cannot explain away the TV/Radio lag as easily. Other than to say they too don't have the population density thus the revenue to upgrade. Plus the economy has been down the toilet. I believe many think that TV/Radio transmitting may be going down the tubes. Cable TV, Satellite TV and XM Radio are putting the hurt on conventional TV (VHF/UHF) and Radio (AM/FM).

You could argue that it's partly due to the same reason - lower population density increasing the broadcast cost per subscriber. The only broadcast system that overcomes low population density is satellite, but that has a huge barrier to market entry.

I'd argue that a lot of it is due to the FCC screwing up all the time. The amount of competition in the market is decreasing constantly. In 1983 over 85% of US TV programming was produced by small networks, either local or independant. That figure has dropped to around 20% today, with the big national networks (ie ABC, NBC etc) producing the rest.
The rules on media ownership were relaxed in 1993, resulting in Clearchannel owning the vast majority of radio stations. The FCC is due to vote on further relaxing the regulations again, which would make it easier for a company to effectively own the vast majority of radio/TV/ISPs/newspapers serving a geographical area.
This is not good news for the US. It's already obvious that the big networks avoid issues that they don't like. (For example, this one - CNN and Fox would prefer to cover "Who did the Bachelor choose?"...). BBC News Online reported a 38% increase in US viewing figures during the recent Iraq war, which indicates that people are starting to notice.
What is really disappointing is that Michael Powell (The FCC's Chairman) has rejected calls for a delay in the vote or for more public consultation. And yet the few public meetings that have been arranged to discuss this issue have resulted in thousands of people who are vehemently opposed to further relaxation of the rules. Of the 1/3 million or so emails that the FCC have received on the subject, something like 99% of them have been in opposition.

Arrgh. I'm ranting.