why do so many people blame the parking companies when the revenue goes down ? Advertisers changes strategies, keywords, ppc amounts all the time. This impacts the revenue. Also parking company might show same amount of clicks, but yahoo might only consider a certain percentage as valid. So many people complain that the "domain industry" has a bad reputation, but it is no wonder, because every single day someone calls parking companies, or their upstream providers... scammers.
I don't think that you have heard any of this nonsense from the bigger players.