It's a possibility - it's also very possible that with that many VIPs in the area, they'd been expressly instructed not to keep saluting them - otherwise they'd have been doing nothing but saluting all day :) and not getting on with their work.
Churchill could also pose a dilemma when he was in uniform. He typically wore the uniform of an Air Commodore of the Royal Air Force (and he was entitled to do so because he did hold that rank) but while that is a pretty senior rank (it's one star), it was considerably below his status as a Head of Government. So when he was in uniform, did higher ranking (two star and above) salute him or did he salute them? As I understand it, they never formally worked out that piece of protocol.
You probably already know this but that is Field Marshall Brooke on the left as you view it and American General Simpson on the right.
Brooke is the big guy and Simpson the tall one. I recall reading where Churchill described Brooke as “a hard headed Ulsterman”.