Perhaps, but I think OP's point was that since he already shelled out 40K for an award in F, why did US ask for more for a "choice seat" even if a regular seat was available? Keep in mind that it was a F award, which is supposedly better than any "choice seat" if it were available on a RJ.
LAX
There were no regular seats available for her trip. For 40,000 miles and the $75 surcharge one would think the lack of regular seats on PHX-PSP would be one of the reasons the cost was 40,000 since F on YEG-PHX only had 3 of the seats showing as booked when I booked her in....