Over my long career, I have served as a reviewer for many conferences and journals, in both theoretical and experimental areas of computer science. I have seen conference committees enlist inexperienced graduate students as reviewers of papers in order to meet the quota for reviews. Because conference papers are limited in length, and because a large number of papers must be reviewed within a short time, the quality of reviews of conference papers is generally low. In contrast, for journals, because there are usually no page limits, authors can explain their ideas completely. Editors can choose qualified reviewers carefully.
Reviewers can take adequate time to write thorough reviews.
On the whole, our expectations and standards for timeliness in journal reviewing in computer science are abysmal. I find this situation deplorable, and I challenge all of us leaders in computer science to educate our students and younger colleagues about their obligation to return timely, thoughtful reviews. Journal publications benefit both the authors and the discipline. By polishing a manuscript for journal publication, the author minimizes the number of errors and improves the clarity of the exposition. Thus, journal papers are more likely to be correct and readable than conference papers.