I'm a bit skeptical of the contention that the psion is more effective in a one encounter/day basis than the wizard is:
In practice, most combat encounters rarely last more than five or six rounds. Five or six rounds per encounter means that the Psion can spend his full manifester level in powerpoints each round and not run out.
But A self-respecting specialist wizard (and psions are essentially specialists), is going to have at least five or six spells of the two highest levels he can cast. And because spell scaling is free for many wizard spells, he can use his 2nd highest level spell slots for direct damage spells and other spells that scale well. That means that the wizard is essentially doing just as well as the psion for the duration of the combat.
If your running 2 combats before resting, then the psion is going to come out ahead somewhat, but a one-combat psion is no more effective than a one-combat wizard.