If you are looking up these things, trying to interpret them, and then passing them on, Gary, I think you have to be very careful not to overstep what you understand--You have made some good points, but you have also said a number of things that, if not exactly wrong, are not exactly right either--There is a difference between situations that use a V chord, and situations where a V7 chord is used--often, the V is followed by a V7--Any song whose melody falls within a diatonic major scale(The C scale, for instance) is a three chord song, because an accompaniment can always be written using only three chords--the I,IV, and V. the IV7 and IVm technically take you into another key--Not that you can't use these things alternately as a matter of taste, but that they have rules and reasons--
For that matter, there *are* notes between E and F and B and C, but the reason that there are half spaces in two places in the scale simply is that if you use all whole steps, you only get six notes to the octave, and no perfect fifth or fourth--
Anyway, and this should extend to everyone, don't speculate on things that you aren't sure of in your explanations, because it only makes things more confusing--