The problem is that not every part of the country has a resistance problem so to address it as though they do is only going to cause more of a problem.
I have been doings things differently when de worming my horses for about 12 years now. I have never de wormed every 6-8 weeks. I have only de wormed for what was needed and only when the count was up there. The only exception is with foals they get de wormed very 30 days for the first year and broodmares about 3-4 weeks prier to foaling and then 2 days after foaling.