At this point, I'm not even sure what your point is, since you said my examples were bad, and now seem to be saying that your initial criticism doesn't apply to one of my two examples, and that you wouldn't compare the two examples I gave with each other.
My point is, that there are scenarios when closed messaging networks are acceptable, and there are scenarios when they aren't, but despite of that, people tolerate them in case of IM, which allows various messaging services to get away with it. I said that I really don't understand why that happens, since in case of e-mail they don't tolerate it.
Hangouts, FB messaging and etc. are generic cases, not the ones which should be acceptable as confined environments (like your example of the forum messaging).
