Hi HC, the whole thing hangs around the typical use of weasel words like 'Avoid', it doesn't say 'Prohibited'. If as you say we expect any icing in the TMA then there is a little line in the QRH which asks us to increment the approach speed by 10 kts in case we believe there is ice buildup on unheated surfaces. If the ice detection system picks up any deposit then the 'Severe Icing Detected' warning is in amber - not red, indicative of the level of threat that Airbus sees in the situation.
Also as you indicate, the deicing system doesn't accelerate and decelerate on an Airbus by 130kts 280 times a min, also it is rarely the system it's self that causes the problem but some primary failure leading to the restriction of available bleed air, since this is what typically does the removal. I suppose on that basis - that little tailess reaction helicopter the French built - the Djinn I think it was called - should remain pretty ice free no matter the circumstances (unless the engine failed, then it's pretty cut and dried)
Generally though there is plenty of warning that you are liable to encounter icing from other traffic and the ATIS and typically we find for out ops that this is only a couple of thousand feet thick.
TOD