You seem to be confusing correlation and significance. Having lots of data points makes the correlation more significant, it does not make the correlation stronger.
No, that's not correct. You can't conclude anything from looking at a big blob because you don't know the density of points at different places in the blob. This is the point the guy you replied to was making.
As an extreme example, imagine a billion data points that fit perfectly on a straight line. Then superimpose a million data points randomly on top of it. What does it look like? A big blob. But almost every point is highly correlated with that straight line.
I agree that a scatter plot is not the best for showing data with that many data points, but frankly it's kind of irrelevant. The point the author was making was just that it isn't that hard to cook up some data that is not highly correlated, but will be if you bin and average it.
See the discussion here: http://news.ycombinator.com/item?id=4027337
I stand by the claim made in my blog post. Don't use scatterplots, use a density plot instead.
Incidentally, according to a comment the author made, the correlation is actually 0.3. That's far better than his graph suggests.
I might add that discussions like these, Illustrate a broader problem with the hacker news community. Rather than discussing the facts of the story, many of the posts are instead about the less relevant detail about how the author chose to present them, despite the fact the the authors point is still effectively made (and if the 0.3 were included there wouldn't have been any doubt)
BTW: tmoertel did some analysis on the data: http://news.ycombinator.com/item?id=5125851 and the correlation appears to be around 0.2, which is pretty weak.