Difference between File Scavenger and Recuva?

Why does File Scavenger pick up so many more files than Recuva? I had to use File Scavenger once to recover a Keepass database file because Recuva and Restoration wouldn't do it. The disk got reformatted by accident (long story) :(

This is still in beta (testing phase), so you can expect it to miss stuff other completed (mostly tested) programs find.