It is said because you burn your glycogen stores while doing the strength so when you get to cardio, you are burning more fat stores. I have followed this, since I first learned it. I do it per my own preference. Also, I've been reading lately, that it may be not as beneficial to stretch out those muscle fibers before strength training, as once believed.
Personally, I sweat a whole bunch! I can't do a weight workout after I sweat with cardio. Talk about slippin' and slidin'.
Marla