Sorry but they are not the same thing. I report how many more homes sell than hit the market but that isnt always reflected in homes on the market on a 1:1 basis. Two reasons are houses fall out of escrow (thats a +1) and houses get taken off the market (thats a -1). There are more reasons and this is not a perfect data set. Real estate data is self reported by thousands of realtors and every house/situation is different. Its why i always advise looking at all real estate data from askew.
It was never intended to be a hard and fast measure but multple measures to understand the direction and velocity of the action in the market. Does that make sense?