Actually, looks like it does pretty well on reads. It's the writes that mongo can't handle. But we all knew that already...
How dare you! The Emporer looks magnificent in that robe!
They appear to have conducted these tests in 1Q12. The versions of MongoDB (2.0.5) and hbase (0.92) both date from then (MongoDB is now at 2.2.x, hbase 0.94.x).