I always thought this was a good example of "common sense farming". You feed a herbivore the brains of another of it's kind to save a few bucks, and after a few decades of doing it something starts to go really wrong. Surprise, surprise.
Still, statistically, your chance of getting mad cow disease, even if you actually eat infected beef, is pretty slim. A hundred or so people isn't a statistical anomaly, though, so there is a danger if you eat enough of the stuff.
But what's perhaps more disturbing is that there is likely a lot of mad-cow infected (if you can really call a molecular disease an infection) cattle in the US, and the meat industry may just not want to test for it for fear of a scare. Even if it's only a tiny chance, I'd pay a bit more personally for meat I know won't give my kid a wasting disease--wouldn't you?
A different perspective:
I watch the Japanese news daily, and in Japan they're a lot more concerned about "clean" food than Americans apparently are. They used to import a huge amount of beef from the US because it is relatively cheap--used at fast food resteraunts and the like. After the first recorded incidence of mad cow in the US, the Japanese got very skittish about US beef. The Japanese government, under heavy pressure from the public, refused to allow the import of beef that wasn't tested for mad cow.
The problem? The FDA and industry organizations responsible for overseeing the testing process refuses to let any exporter test all their cattle--only whatever "good enough" percentage is currently required to be tested. This hurt a lot--many inexpensive resteraunts in Japan, such as the famous "beef bowl" chains (beef strips on rice) literally had to completely reorganize their menus, because of the lack of inexpensive beef available for import. Some of the slack has been taken up by Australian ranchers, but apparently Australian beef tastes different enough that a lot of Japanese just don't like it for whatever reason.
For months, the Japanese news has been reporting on this constantly, and they've run investigative stories where, for example, a cattle export company wanted to test all their animals, but they were indirectly threatened by a major organization (I think it was the FDA, though it could have been an industry organization) if they did so. They've also had several interviews with ranchers who had cattle die under very suspicious circumstances, but after testing were told "Nope, not mad cow disease, don't worry." "This isn't the first time this happened." was one rancher's comment.
Could just be paranoia, but it seems awfully suspicious, particularly considering that the government of Japan seems more concerned with the health of its people than ours. What would the problem be with testing every animal? Yes, it'd be a bit more expensive, but not enough to make a huge difference (a few cents a pound) to anybody but the rich factory farm executives... unless there's a big chance of actually finding a whole lot of infected cattle, which would be disasterous.
Personally, just in case, I stick to locally-ranched, non-antibiotic'd, free-range, grass-fed cattle. I can go watch 'em eat if I want, and it's a whole lot more humane to both the cow and the person eating it than those huge reeking factory farm "ranches" I drive by on the way to LA.