What's funny about this (apart from your excellent joke) is that there are actually a lot of places, where they are a common crop, where bananas are advertised as "boneless". This is because, I believe the bit that connects the banana bunch to the plant (not a tree!) Is sometimes called the "bone" (I believe it's "C" in this image:

Having the grocer machete this bit off for you presumably cuts down on the unnecessary weight on your moped back home, and maybe even the costs, if buying by weight.

Caveat: This is just what I have come to understand, from travel experience and curiosity. If there are any actual "Bananologists" about, please feel free to correct!