文末の "A as well as B"、"S V ..., while S' V'...."などの表現

本来その後に比較的情報価値の軽いものを導くとされる以下のような表現形式が、文末でカンマのあとにおかれ、その後に実際には情報価値の重いものをもってくるというものをよく目にします。

(a) “as well as” (例) Picking up the latest copy of “Imidas” or “Gendai Yougo no Kiso Chishiki,” available throughout the year or a reasonable [\]2,500, is an excellent way to stay up to the minute on new Japanese words, as well as on the many facets of modern Japanese life reflected in them. (ある英字新聞の“KANJI CLINIC”というコラムから)

(b) ”not to mention” (例) He has two big houses in this country, not to mention his villa in France. (Oxford Advanced Learner’s Dictionary, 6thから)

(c) “though” (例) They are very different, though they did seem to get on well when they met. (上掲のOALDより)

(d) “while” (例) Schools in the north tend to be better equipped, while those in the south are relatively poor. (Longman Dictionary of Contemporary Dictionary. 4th から)

これらの一連の表現パターンが、文末で、しかもカンマの後に現れる背景にはどんな仕組みがあるのでしょうか？