>I was wondering why haven't been there any discussions of phrases, idioms etc ?

actually®, there have been a great many such, but as there is no specific category for them, just try to find them! there are lots of sites that cover these (just as there seem to be lots of sites for everything) and some good ones like "Word Detective" and Quinion. but when you don't know where to start, the best ploy is to plug the phrase (in quotes) plus the word 'origin' into google.com -- try it with "saved by the bell" and see what you get.

btw, you prolly won't like what Quinion has to say about this phrase -- in a word, he says this story is "hogwash".
:-D

http://www.quinion.com/words/qa/qa-sav1.htm

(post no bills)