Hasn't anyone listened to the ATC tapes? You can clearly hear "go around" called when Asiana is on short final. That "go around" was called by the UAL flight crew holding short.
On the clip I heard, it sounds more like
''San Francisco Tower, Skyward (?) 737 (go around), 1,500 feet over San Carlos (?)''
The 'go around', if transmitted by the UAL, appears to be made when someone else is already transmitting, so it may not have been heard anyway. It is of such short duration with no reference to who it refers (callsign or type), that even if it was transmitted with the best of intent, a pilot might not work out it's for him, especially if not a native English speaker. Consider also that the Tower has multiple arrivals to multiple runways, with aircraft being cleared to land with other aircraft ahead, and the simple call of 'go around' with no other information could cause multiple go arounds as well as confusion as to who it was actually referring to.
The other problem with these clips is that they are not necessarily in a proper chronological sequence and the time can be compressed. They also seem to have transmissions from several different frequencies all jumbled in together. None I have heard are very helpful to the armchair investigator.
The NTSB will have the ATC and CVR tapes, which should be much clearer and easier to interpret than some of the internet offerings. No doubt their findings will come out as the investigation progresses.