which version are you girls using?
I am using DDR extreme 2. I can't say difinitively, but it wouldn't make sense for any of the DDRs after that to not have that function. Try stepping on the mat at the beginning of a song before any of the actual step arrows come up. If the corresponding arrow on the line at the top glows when you step on it I'd say its sensing each and every movement. You should see a little fluctuation on the calorie counter as well. Someone on the forums at getupmove.com might be able to tell you for sure about your version.
I too hate exercise. I had been jogging but the weather here (nova scotia) is cold enough to make me not want to bother. Also, I am pretty much terrified at this point of going to an actual gym so I would also like to know if DDR will be enough to see me through these winter months.
Something I have been wondering about is the accuracy on the step counter. How in the heck do they know that one step is worth .093 calories or whatever? And can I trust the accuracy of their tally??

I usually shortchange their count when I put in an equivalent on fitday.com just in case.