To those that say the wizard at will are already strong, consider that the wizard has terrible AC, hitpoints and healing surges, and that his at wills hit allies in addition to enemies. He has fewer options to avoid or mitigate OA's, and he doesn't have the defenses to risk many. In other words, more powerful at-wills may be a means of compensating; they're better compensation than more powerful encounters or dailies since they're useful more often, but also since they're less easy to obtain via multiclassing. After all, you want to avoid the situation where the best "wizard" is actually a different class multiclassed into wizard.
Balancing offense and defense isn't easy, but it's necessary if the game isn't to become monotonous. 4e already errs rather heavily towards same-ness between classes (compared to 3.5), and while this is good for balance, it's bad for diversity, so I don't think the appropriate response is to balance the at-wills of every class.
So, while such overall class and role balance might not be easy to find when crucial aspects such as at-wills diverge, it's important they try.