The Warforged are not too powerful. They are, however, annoying.

Because that +10 Fort save and that Delay Poison and that suit of armor all represent something for the player sthat have them: they spent rescources to get it.
The Warforged does not have to spend any rescources to get their immunities. They're just BETTER at it. They have to spend extra rescources for other things (healing, armor, etc.), but this doens't make them any easier to integrate when you're challenging certain things that they can do.
Eventually, that cleric will run out of spells. Eventually, that sinking fighter will have to make a choice. A Warforged, however, does not run out of immunity and does not have to make a choice. When a campaign is focused on whittling down the PC's rescources to the point where the players are feeling the tension of the encuonter, the warforged will miss the entire point of it, because he will never feel the tension. That +10 Fort save may be great, but that 5% chance of failure keeps the sweat on the brow, and not every poison has the same DC. The Warforged have no fear. And that changes how you have to arrange the game. You have to accomodate the Warforged in ways that you don't have to accomodate normal air-breathing, poisonable humanoids. In order to evoke the sense of danger you want the PC's to be feeling, you need to constantly be reminded of the fact that the warforged player just isn't in any danger. Yes, there is still the risk of failure, but when the goal is to fear for their lives, failure is a pale substitute. Warforged are immortal. They can always try again.