The other two elements can probably form clones, but as you remember in the Kakashi vs Pain arc, it took a great deal of chakra for Kakashi to form a lightning clone...and it was hardly more effective than a regular shadow clone.
So, perhaps Fire and Wind style clones take up too much chakra...
I should really think this one through a little bit more,(I'm not really convinced myself) considering everyone else's' theories get bashed pretty hard on here...
Looking at Madara's character throughout the anime, it's difficult to take him literally because he is an unreliable source of...