Maybe they can't impact the bitcoin price,but they CAN for sure manipulate the altcoin prices,especially the small penny altcoin prices.
And that where those manipulators/speculators pump-and-dump groups really do their thing. We all know that altcoins markets are haven for those kind of greedy people and people have been warned, however, but whatever reasons, many are still failing for the trap and later will bitch around saying they have lost so much money. If they would just go and invest on Bitcoin then they wouldn't have this head-ache.
As for Bitcoin price or fake volume tradings, yes, it could have been fake and ballooned by some trading exchanges but most of the time it wasn't very evident because of the continuous flow of money in the bitcoin market. So @figmentofmyass, said, it doesn't really matter, arbitrage for one is a true testament on how the spread can be cover up.
