This SL page is based on Charles Matthews' article at GoBase. - Floris Barthel?
is designed to limit Black's future expansion on the bottom side.
If Black completes the Chinese fuseki now with a or b, White will play at one of the marked points.
Therefore, it is customary for Black not to complete the Chinese formation, but instead to continue as in the following diagram:
prevents Black from ever getting the chance to finish the Chinese formation.
Charles I didn't have a computer database when I first wrote about this, two years ago (see http://gobase.org/studying/articles/matthews/fuseki/14/). In a sense that's better, from the point of view of discovering things: more sense of achievement.
What I now see is that the most recent case of Black completing the Chinese-style formation in a pro game was 1992. The approach (low or high) in the lower left is completely dominant.
I have edited something out from the first diagram, that I didn't understand.
I think this was being said: assuming ,
is a good point because White at the square-marked point is ideal.