That's a nice post hoc rationalization but in practice it doesn't actually come up. I don't have any other app with the same semantics as Gmail. For instance, what app combines forward/next navigation with selecting, labeling and archiving? Unlike vim which I miss in native text fields, there is no context outside of Gmail that the muscle memory wants to kick in; the corollary being that there is not a comprehensive set of OS default shortcuts that maps cleanly to the set of things I want to do in email. In fact Mailplane does attempt this for Gmail so you get ⌘-n, etc, but the common ones are really not sufficient to cover a power user's email workflow—you're going to need to learn a few things specifically for your client of choice regardless of what that is.