There could be a number of reasons for his cutoff but the primary one is probably that what ever you report as resources should have a reasonable chance of ecomomic extraction as per NI43-101. In the case of Cow Mountain I beleive the ore is to be milled and that there may be a fairly high strip ratio. At $1300 gold price (a common resource reporting number now) 0.6 grams of gold is worth $25. So you need to mine it, process it and deliver it for less to make a profit - and this takes into account operating cost only - no capex if a mil is to be onsite (trucking to QR would render lower grade materia uneconomic as trucking alone is about $19.00 tonne). The comparison to Victoria Gold (Dublin Gulch for those who remember) doesn't work as it is a large low grade deposit (~1.0 g/t) that will be open pit mined at a high rate of tonnes per day and heap leached, a much cheaper processing method.
The assumption that a lower cuttoff brings in more ounces is just that - an assumption that what is currently defined as waste is actually mineralized - when it maye well not (and probably isn't). Also if you want to add 8 million ounces of low grade material to the PG resource (already way to high IMO) then at a grade of 0.6 g/t you would need there to be 415 million tonnes of material. I think that if there was such large low grade deposit present that it would have been identified already - which has not happened.