I agree with the underdosing on dewomer - not that we want to o.d. them either. I know we give not quite a double dose but maybe a dose and a half on all adults - smaller 300 larger 500 as the heaviest mini we've had on a scale was 350lbs. Foals we do at 100lbs until they're over that weight.
Ivermectin is VERY safe if overdosed. I have had an experience in the past when a foal got the WHOLE TUBE in error (full sized horse foal). The vet said not to worry, it was quite safe, and he sure wont have any worms! They have also tested it in other ways- letting it sit in a hot car for months, then testing the contents, etc... not that I would recommend that, but was told it passed with flying colors.
Just edited to note though, that I agree, I dont like the 'suggestion' of the article!! Then what?!!