From the release notes:
I'm not positive why this change was made, maybe it's to cater to the WoW crowd because this screams of a system that would be used there.The spell damage amplification system (including bonuses from items and enhancements) now uses a Spell Power rating to determine how much damage you deal with spells. In most cases, each point of Spell Power increases the base damage of your spell by 1%. (For example, casting a spell with 100 Spell Power will result in double damage.)
Unlike the old damage amplification effects, Spell Power is not restricted by spell level, and bonuses to Spell Power of different types stack, following standard D&D stacking rules. (An Enhancement bonus and an Alchemical bonus will stack, but only the greater of two Enhancement bonuses will apply.) The bonus damage from Spell Power is not multiplied by metamagics such as Empower Spell or Maximize Spell.
Items and enhancements that granted damage amplification to specific damage types will now provide a bonus to Spell Power with spells of that damage type. (For example, an old Combustion V item that used to grant +20% damage to level V or lower Fire spells will now grant a +48 Equipment bonus to Spell Power when casting any Fire spell.) Potency effects grant Spell Power with any spell, as expected, but generally have lower values than specific effects.
In my eyes though, this looks really awkward...
In bold from the release notes, apparently 1 Spell Power = +1%... well why do items give odd values like +48 and +108.. are we getting +48% and +108% or are these values more closely rewarded with +40/50% and +100/110%?
One thing I hated with WoW was the numbers were not intuitive all the time, you just had to get them as high as possible and know that higher is better, which is what this looks like...
I don't know why they got rid of the old level restrictions either... change for the sake of change?