I don't want to get too much into the politics of it (I hate agility politics), but there are BCs running 16" who have no business being in that height class. They get favourable measurements from VMOs who are biased towards BCs, people know who these VMOs are and will seek them out so they can get their dog into a height class they shouldn't really be in to make it easier on the dog. I'm not even talking about dogs who are borderline, I'm talking dogs inches off. Some of these VMOs also measure any non-BC high... so the BC gets WAY lower than it should be and any other breeds gets way HIGHER than it should be...
There are some actual petite BCs who truly belong in the 16" class, don't get me wrong, but there's also fudging going on. A few years ago at a regionals or nationals, I forget which, the judges announced that ALL dogs would be measured before they ran. There were BC people who immediately packed up and left, because they knew they would be caught running far lower than they should have been. They didn't even wait for the measurement to see if they could squeak by... they just up and left.
Funny enough, IIRC, the announcement was actually due to hubbub over Aussies, NOT BCs. =P This was when people were pissed about "mini Aussies" registered as Aussies and running 12".