That, too, may be somewhat of a non-issue: the MC feats make the granted AW power into an Encounter power for the PC who took the feat. Essentially, he burns a feat to gain a few benefits, one of which is an underpowered Encounter power.
I'm just asking if they can upgrade that underpowered Encounter power for a higher-level- but still underpowered- Encounter power.
(Currently sitting in a doctor's office, nowhere near books- no clue as to other classes' AWs and the like- nor whose AWs scale with level, etc.)
The wizard MC feat states that you can take a wizard at-will and use it once per encounter. It doesn't make that at-will into an encounter power...
OK, now this is different.
While I really don't agree with the logic here*, I've encountered it in other corners of 4Ed's design. It is, at the very least, internally consistent with other design decisions.
That makes it a rationale I can live with, even though I don't agree with it.
* I'm very much a "walks like a duck"/"distinction without a difference" kind of guy.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.