Theoretical computer science is much like mathematics. But virtually no other area in computer science is, even slightly.
If you look at computer science papers in machine learning, systems, human-computer interaction, networking, robotics, or architecture, you'll almost always see an experiment of some sort. These are typically benchmarks, but there are plenty of other examples of empiricism in computer science.
But the experiments in computer science are horribly designed! They lack almost any control, and use statistical methods that would make psychologists wince. Hypothesis testing is rare to the point of nonexistance. (Psychology sometimes adjusts too far in the other direction, using complex analyses where a simpler one would do.)
Further, experiments are nearly never replicable, at all, because the systems evaluated are never made public, or the experimental environment is never recorded. For a great treatment of this trend in systems, see http://www-plan.cs.colorado.edu/diwan/asplos09.pdf. Pointing out a systematic artifact in that many experimental designs would be career-making in psychology, or any other science! But you can look at modern papers and see exactly the same mistake being made.