Var effects the HPTA. But it does so to a lesser degree than other AAS. In one study, as little as 15mg/day, caused inhibition to occur within 3 days. This means that levels of LH and testosterone decreased after just three days.
Now tell me what 30-50mg/day will do if you run in for 4-8 weeks. Same goes for Primo where it is regulary stated that it does not effect the HPTA.
One point to consider is that inhibition and recovery time varies considerable from person to person. So it is possible for some people to take x amount of something and not be affected by it much while someone else is effected to a much greater degree.