Obviously, Saeviomagy last saw psionics used in a 2E AD&D campaign with 'Psionics Are Different' style used, and someone playing a 2E psionicist with Disintegrate at 3rd-level or something. {:^D Last time I saw it in 2E, yeah, one of my friends played a 10th-level psionicist who kept Disintegrating small chunks from the colossal golem we were fighting, whom none of the magic-users could affect because of golemic immunities and Magic Resistance, but then, we wouldn't have survived the encounter if not for him gradually disintegrating the golem's head and torso.
As for 3.x psionics, a psionic character only learns as many powers as they get automatically, based on their class' level progression chart. They cannot unlearn old powers to replace them with new ones. That's part of what balances a psion's flexibility compared to sorcerers and wizards, the fact that psions are even more limited in powers known and so they have to choose and apply creatively. I dunno if the Expanded Psionics Handbook has any feats or whatnot to learn new powers (I haven't bought into 3.5 yet, my 3.0 books serve me well enough so far), but as someone mentioned, one of the Dragon Magazine issues featured some XPH-related materials which included the Erudite psionic class. ......Let's see, the issue was 319, May 2004, the Dark Sun issue. The Erudite can learn many more powers.
The meditation description just described how they learn their new powers each level, just as a sorcerer gains new spells as inspiration or something. It was just flavor text. Each time a character levels up in a psionic class, they learn new powers as appropriate if the progression chart shows them as having more powers known at that level.