It is easier to make a Transpose that works on Association of Associations than List of Lists. The difficulty is on ragged srtuctures. For example what should be {{1},{a,b}} transposed ? It can't be {{1,a},{b}}, because this is allready the transposed of {{1,b},{a}}, It could be {{1,a},{,b}}, but in that case the transposed of this later form would be {{1,},{a,b}} which is not equal to the inital form : {{1},{a,b}}. With Association of Associations there's no such problems.

All this to say that the generalised form of Transpose is easier to develop in the case of Association of Associations.

@Silvia this is supercool Silvia :-) -- I sent you an email about it.