@jcj:
I think the qualifying words are "The loss of *these* data" - meaning more than one of them [EDIT : and as if789 correctly points out below - permanently], an example of which was the Aeroperu 603 accident. Or a situation where loss of one has knock-on effects (like Birgenair 301). As long as you're (relatively) straight and level, temporary loss of airspeed data can be easily overcome by using pitch-and-power, which is the reason smaller aircraft which don't have any redundancy in the pitot-static system can still pass airworthiness requirements.
In short - the temporary loss of airspeed indication *alone* was not considered a threat because there were long tried-and-tested workarounds.
Regarding the FAA's point on replacing the Rosemount units, I'd like to see the original document if anyone has a link handy. They may have been thinking along the lines of Birgenair, where a blocked pitot tube on one side caused the automation to pitch the aircraft up to the AP pitch/AoA limit due to a false overspeed condition. Even in that case the aircraft only departed controlled flight when the PF (Captain) pulled the throttles back to further reduce speed and immediately put the AoA into the stall regime.
The Airbus systems automatically disengage autoflight if the data from the three pitot sensors disagree, so a similar situation would not happen there.
Last edited by DozyWannabe; 19th Jul 2014 at 00:13.