I get the impression that many people confuse the use of asanas to produce certain results (the same mechanism for ritual is in place in this case; the association between a cause and an effect) and when ideas get transmitted from system to system things like these get disseminated, in error, in my opinion. Hence the connection with sitting on the ground with enlightenment, because 'that's how the Buddha got his'- but of course we know this is not that simple, he went through a lot of experimentation and research, and the sitting under the Boddhi tree could have happened anywhere, when he was ready. If it really did happen that way. But I digress.