A lot of the powers were changed with errata - check the Updates file for any discrepancies.  Most changes are small things, to prevent abuse or clarify confusing wordings, but a few things changed significantly (for instance, the wizard's Magic Missile does a little less damage and does fixed damage instead of a roll, but is an auto-hit).  Also, the D&D Essentials added a handful of changes to existing things in the PHB (for instance, a lot of classes now have a small choice of what ability scores to boost with their racial bonus.)<br/><br/>Yeah, it's a little confusing, especially if changes to an item or power are in a book and not in the official updates (for instance, a spiked chain in PHB1 is a normal two-handed weapon, in the AV it's a double weapon, and the change isn't mentioned in the updates).