In all of those cases the guys there was a reason for someone to trade them. Usually the team that had them couldn't afford them and was looking to get something for them before the trade. You can add Percy Harvin to that list too, he went for a first third and seventh.
The reason I said there's confirmation bias is that buyer initiated trades are rare. Usually the seller needs to get rid of a guy. So most of the trades tend to favor the buyer. Buyer initiated trades are often lopsided the other way - trading 3 firsts for rg3 or your whole draft plus for Ricky Williams (both rookies but that's not the point), two firsts for Joey Galloway, and so on.
But if we tried to peg the value of ty Hilton, the price would depend on who was asking. If the Colts tried to move him they might not be able to get a first. You're right about that But if someone else for some reason decided that Hilton was the best player in the NFL, they'd have to offer a lot to pry him away from a team that wants him and needs him, probably more than a first and certainly more than it would have cost if the Colts had initiated talks.
We only see trades that happen, and trades usually only happen when there's an issue forcing the owning team's hand. And that's what's happening here with cooks.