Not sure if this is quite what you want, but the "Show Past Answers" button can be used to get information about more than one student. If you view the past answers for one student, you will see at the top of the page that there is a form with the students name, the set name and the problem number. You can use "*" as a wildcard (and I think even regexp syntax as well) to view more than one student or more than one problem. Putting "*" in the student name and in the problem number will get you all answers for all students for all problems on the given set. The format may not be what you want, but it gets the information.
Certainly, the past answers page could be made more flexible and informative.
Davide
WeBWorK Main Forum
Downloading a file containing student statistics and responses for all problems in a given set
This forum has a limit to the number of forum postings you can make in a given time period - this is currently set at 10 posting(s) in 1 day