No, the power books give you extra options in the class features you can take. Tomes for wizards for instance, however, the way you build the class is the same and the say way as all classes. Pick class, pick optional class features, pick powers, pick feats.Ok...I'm not being snarky...but your first paragraph..um, isn't that he exact same thing from the Powers book?
Didn't the powers book introduce new class features/builds for all the classes of that power source?
Am I looking at Martial Power 3/Arcane Power 2 here?
Essentials in the preview wizard gives you class features at level 1,4 (apprentice mage), 5,8(Expert Mage), 10 (master mage) or in the case of the cleric encounter and daily powers seems to be set by the choosen Domain.