A character’s initiate grade cannot exceed her Magic attribute. If a character’s Magic is reduced below her initiate grade, she loses that level of initiation and the metamagic she gained with it.
Agreed. However, a character's Magic may exceed her Initiation grade and then be lowered to be equal to her initiation grade without effecting initiation grade. A Magic 6 character can have Initiation 6 regardless of whether or not he once had Magic 12. As this theorietical cyberadept grows he has to be sure that there's always room to keep his Magic one point higher than his Initiation Grade. He doesn't have to buy it immediately, but he does have to have room to fill Magic=Initiation Grade+1 at some point in the future.
Put another way:
At character creation, cyberadept has Magic 5, buys 4 Essence worth of 'ware. Now he has Magic 1. He has the potential here to spend 25 BP to get Magic to 2.
Later he pays Karma to get Initiation Grade 1. He can now buy his Magic up to 3 if he wants (paying for it as an increase from 5 to 6 then from 6 to seven).
He gets another point of 'ware, reducing his Magic 3 to Magic 2.
Later he gets Initiation Grade 2, buys his magic back up to 3 (6-Essence loss+initiation, paying for it as an increase from 7 to

Now he goes back and forth, buying one grade of initiation, then the point of magic to fill it through grades 4-6, ending with Initiation 6 and Magic 7.
Adds .99 worth of 'ware flushing his essence down the toilet.
He now had Magic 6, Initiation 6 and 5.99 Essence worth of 'ware without his initiation ever having been higher than his Magic.
And in the case of the optional rule of Power Points instead of Metamagic he also has 12 points of Adept powers, supplementing the ones that are maxed out with 'ware that enhances them still further.