This particular order of precedence was used so as Andrew and Fergie did not walk alone together and be uncomfortable up front like that- it also hints of a warmer welcome than many other public outings They both have had scandals and are keen to redeem themselves.
It still doesn’t answer why Anne was not up there instead of her husband.
I didn’t see any positive comments about Andrew strutting up there like that. There may have been some but it was overwhelmingly negative.
Many thought William didnt show up because of Andrew but it could have been as simple as he was sick.