A long time ago I saw this question, and the reason for the slowness of the Ruby is that it loads the entire CSV file into the memory at once. I have seen some people overcome this issue by using the IO class. For example take a look at this gist for its self.perform(url) method.
For the 1.8.7 Ruby that Eric is using, it might be :)
I think that using CSV is little bit overkill for this.
lol I totally overlooked that. I was convinced that CSV.foreach is loading firstly everything to the memory.