The point is that even if it gets corrected on a high-profile site or two, it enters into the collective consciousness and sticks there. Kind of like Reagan's welfare queen example.
I think you've proven my point. The non-blogospheric welfare queens are, I daresay, still stuck in the nations consciousness, lo these decades hence, and all without the help of the internet. Of course falsehoods are propagated and stick in the blogosphere, but not any more than in any other medium and, perhaps, less.
The amusing bit is that there is no misinformation in John Derbyshire's original article. Like so many arguments (this one is about the Irish famine), it is a debate between the numerate and the innumerate. Derbyshire points out that the population of Southern Ireland had quintupled in 40 years - a rate of growth to be seen nowadays in parts of the world where modern medicine and an adequate food supply is combined with a total absence of contraception. To quote:"A thing like that is hard not to notice. And yet, within the political thinking of the time, nobody, not even the best-intentioned and most charitable observers, could think of anything to do to avert the coming disaster. " In fact there was nothing that could have been done.