I want to leave a comment and to correct it here:
It is meaningless to compare the two groups, they target to different applications. I think the post just make more confusion. And what Mr. Stonebraker said is also not right.
I think the only thing which make these confusions is the term "column" in Group A. In fact, it is not traditional "column" of RDBMS area. And your example of a traditional spreadsheet table is also not the real target of Group A. The "column" name in Group A is in fact data (not schema).
If have got to change the term, I think we can change the term "column" in Group A to "end-key". In fact, in Bigtable, there is no column, it is "qualifier".
(1) Group A's "column" is in data, not schema.
(2) Group B's "column" is in schema.
They are different in conception and application target.