I know that... let me try to explain a different way:
You have a player, let's call him Speedy McFlawed. He's fast, but raw, so he's projected to go near the end of the 3rd round, or beginning of the 4th.
In a world with comp picks, the Steelers get a 3rd round comp, and take Speedy McFlawed with that pick. In a world without comp picks, the Bears (who have the first pick in the 4th round), take Speedy with THAT pick. By adding the 3rd round comp pick, all you've done is move Speedy McFlawed up one draft position.
This in turn might move another player, Slowey O'Strongman from the 2nd pick in the 4th round, to the 1st pick of the 4th round, etc, etc, until you eventually get to the end of the draft, and the players that have truly been ADDED to the drafted pool are the guys at the end of the draft who would have gone undrafted normally.
If they were adding comp picks to the 1st round, I think you'd be spot on, because that would be adding players who would have 5th year team options built into their deals. But whether a guy goes in pick 104 or 105 really doesn't change anything.