[JPLeRouzic]

That is not true, all newer (than 802.11b) frames are encapsulated in a 802.11b frame, precisely to be compatible with it. At IEEE there are always discussions about to drop compatibility with 802.11b but usually someone reminds that in fact it is not a real problem.

What is a problem is that the preambule time is wasted, but it would not be too hard to imagine that even this preambule could be used for newer amendments after some homework.