Why does Dependent Care FSA show up in box 10 on W-2?

At my work I can do an FSA for health and/or dependent care.  If you don't spend it then you lose it- that's the way a FSA works.  So the FSA for health is only informational on the W-2 but the FSA for dependent care is in box 10 and counts.  Why is this?  They are both use or lose.  Say I don't spend anything from the dependent care FSA.  I've lost it- it's not income for me.  Why is it in box 10?