Why does the number of publications for computer science and economics PhD students differ by so much? As a CS PhD student, I'm often surprised at how few papers econ students have when they go into the job market. Even students at top universities typically have 3-4 papers, mostly still unpublished, whereas it is not uncommon for CS students to have more than 10 papers by the time they graduate -- some CS undergraduates already have 3-4 papers or more. As this blog post confirms:


  CS candidate typically have many papers while economics students typically have only a few polished papers.


I can see a few reasons that contribute to this, but I don't think they satisfactorily explain the phenomenon. 


Econ students often spend the first year only focusing on classes and qual exam. However, a 1-year difference in a 5-6-year program is not that much, and CS has classes and qual exam of its own, though admittedly more relaxed.
The publication venue for econ is journals whereas CS publishes in conferences. However, top CS conferences usually have acceptance rates of 15-30% and people spend a lot of effort polishing their papers before the deadline, so I'm not sure how much more polished econ papers can be, whatever "polished" means. Moreover, many CS conference papers are turned into journal papers without major additional contribution.
The econ job market places a great deal of importance on a single "job market paper", so there is less incentive to work on other papers. However, wouldn't other papers to go along with the job market paper help toward a better profile? Even if econ students don't want to start big projects, there are journals such as Economics Letters that accept shorter papers, whose website even says explicitly: "especially young researchers and advanced graduate students are encouraged to submit their articles."


As I said, I don't think the reasons I described satisfactorily explain this huge difference in number. What am I missing?
I don't believe what you say is univesally true of all CS areas; it is certainly not true of mine. But more to your point, based on my conversations with colleagues in economics, one factor (possibly of several) is definitely the submission-to-publication delay: A conference turnaround is about three months, but a journal can be much longer, especially if major revisions are involved.

Here's some insight on the subject (published a while ago).