Even at higher levels the heavy armor is not needed.Level 26 wizard with +6 Chain (+18 AC) will have a 41 AC
Level 26 wizard will likely have a 25 intelligence so in +6 leather he'll have a 37 AC.
So 1 feat for +4 more AC at mid epic levels isn't a bad deal for the wizard. It'll also be much easier to have a 13 str by then too.
But at lower levels sticking with leather is clearly the best answer.
Even at higher levels the heavy armor is not needed.
The level 26 wizard with +6 spiritchain will get +18 AC from his armor.
The level 26 wizard with 25 Int and +6 starleather will get +17 AC from his armor+ability-mod.
It's only one single point difference
But it's not just +1 AC, it's +1 AC and -1 skill check penalty and -1 square speedYep, and in general +1 to AC is considered the cost of a feat, so a wizard "might" consider it.
Implement mastery in Staff will grant an extra +1 to AC. So: +4 (Int) +2 (Armor) +1 (Class) to 17... same as Scale Mail. And the ability to increase the AC as an Interrupt once per encounter. Nifty, IMO and no need to waste a 13 in STR to get Hide armor.
Number-crunching aside, the idea to get rid of restrictions on wizard armour is one I'm very glad made it through to 4e.