A wizard that maxes out Intelligence still has enough points for two other stats at 13 before racial modifiers, or three stats at 12 (which will hit 13 in the paragon tier, where many feats like Spell Focus become available).
Implement mastery focuses on one other stat. Unless you're milking Orb Mastery for the save penalty, you can start with a 13 in your implement's chosen stat (DEX, CON, or WIS) and push that stat with your stat bumps. The implement stat is nowhere near as important as Intelligence - you may get an extra +1 or +2 to hit once per encounter with Wand Mastery...but is it worth sacrificing a +1 to hit all the time due to a lower intelligence? Is pushing Constitution for Staff Mastery to be able to avoid one hit per encounter worth lowering your chance to hit with everything, including your daily powers?
The smart move for most wizards is to max out Intelligence with 16 of their 22 points, and use those other six points to fill in the gaps. At worst, you should never have an Intelligence below 16 before racial adjustments, and unless you have roleplaying reasons to do otherwise, you should play a race with an Int bonus.
