I can only relate my perception of this occurring in certain conditions only, where speed and handling aggressiveness is likely quite different than yours, so your experiences may vary.
Regarding wheel building:
Since all spokes are always under high tension in a properly built wheel,
That statement is very much false for metal spokes. Under load, spoke tensions can vary by quite a lot during a duty cycle. Spinergy BPO spokes are something of an exception as they are much more elastic and result in a more uniform tension throughout the wheel during a duty cycle (ignoring other BPO characteristics in this discussion).
To support your argument regarding aero spokes, you would have to believe that spoke gauge plays no part in a wheel's lateral strength. In many cases with an aero spoke, you are looking a sub 1mm thickness vs. 2.3mm in the fore/aft profile. This is done by taking a round 15 gauge DB section and flattening it. However, flattening an aero spoke profile does indeed influence its side-load characteristics and can be simply demonstrated by bending an aero spoke fore/aft, then sideways... there is a substantial difference in stiffness between these to planes whereas a round spoke is obviously going to have symmetrical characteristics. Putting a spoke under tension does not increase its inherent lateral strength.