Chryse,
No problem with your basic explanations.
However, it is endemic in most areas of study, not only flying, that different explanations are pitched at different target audiences and, in consequence, varying levels of simplification/approximation/assumption are used appropriate to the reasonable needs of the target audience. So, for instance, a new PPL student needs a story rather different to that which would be appropriate to a post-graduate level. You will notice that several of the posts make reference to the Mach No. variations (which appear in numerous texts), but not the Reynolds No. variations (which tend to hide in aerodynamics texts), when discussing indicated speed at the stall .. same sort of thing.
One needs to be a little wary when quoting design standards (Part 25 and the like) as the "real" words of interpretation are in the explanatory documentation used by certification practictioners. One ought to be very wary of consulting design standards in respect of a particular aircraft unless the relevant (ie not the current) standard is obtained. These animals are an evolving thing and the differences in requirements over time vary quite significantly.
Vmcg/Vmca
There is no necessarily hard and fast relationship between the Vmcg and Vmca numbers of which I am aware... the point I was trying to make is along the lines that I can't see any reason why one need be higher than the other. Just trying to highlight the dangers in making definitive statements and/or drawing a general conclusion from an inadequate range of specific examples. Perhaps some of our experienced FT brethren might be able to add comment ?
Far more important is your suggestion that the values are only dependent on density... while the certification figures are very tightly controlled it is necessary that the pilot-in-the-wild be aware of a variety of factors which, most definitely, do affect the real values which are going to bite the pilot on the day. Consider
(a) CG
(b) crosswind for Vmcg (as an aside, the 7 kt derives from ancient UK practice .. be aware that US practice is to determine Vmcg for nil wind .. and the actual limitation on the day is VERY wind dependent. Also, depending on the vintage of design standard being used, the centreline deviation may relate to different limits)
(c) bank angle for Vmca (very dependent)
...etc
Indicated Stall Speed
Putting to one side the argument that stall is driven by incidence, not speed, indicated stall speed will vary with altitude. What you have missed, I suspect, is the often/usually ignored variation in CLmax due to variations in other parameters such as Mach and Reynolds Nos. which, themselves, vary with level. CLmax reduces at higher values of Hp and the KIAS increases slightly. Reference to any standard aerodynamics text will bring you up to speed on this matter. It is, however, generally not addressed to any extent, if at all, in pilot texts.