I found 3 cases in my professional database where this sequence was played (out of 3884 occurences of ). Of these three, the sequence of the left (played by Ma Shi (black) against Li Gang in the 1991 Chinese championship) seems most 'standard'. A second game (Hane Yasumasa vs. Kato Masao, 1982 Meijin) went the same, but with at a.
This is the normal joseki. In the variant of Non Joseki Exercise 5, white has a stone at a rather than 9, which is a clear minus. My opinion as to why it is played so little is that white's corner remains rather small, while black gets an opportunity to defend his weakness (by playing in the diagram). White has quite a bit of aji on the upper side here, and in the diagram above, has already made the decision on how to use it.
Why then has white, be it extremely rarely, sometimes played this sequence? I think it is because with this sequence it is hard for black to build a wall facing the left side. Thus, white is forcing black to switch strategy if black's intention were to answer here at 3. -- Andre Engels