I don't think these guys get as open as you think. Burress doesn't get open that much, and people talk about his sick catches but think about his drops too. The Seahawks game he dropped one literally right in his hands and it turned into an interception. The Jaguars game a ball was placed right into his hands and for some reason he tries to tip it to himself and drops it. Would've changed the game.
Both Plax and Shockey are in no position to show up Eli. And vice versa. Eli doesn't show em up though, so it's not an issue. Once Eli becomes a better QB, this will quickly turn into not as big of an issue.