Well there's (2) ways-- hand-picked or "cherry-picked" if you will, or technology (innovation).
Innovation takes a substantial amount of time, and again, its not a guaranteed thing. Cherry-picked is incredibly supply dependent--I know that Low Voltage Opterons weren't available till at least 6-8 months after the Desktop version's release.
Since the G5's have enough problems getting to its customers (think Dual 2.0 release and then Dual 2.5 release and how many actually got it w/in a week of placing their order?); I don't think Apple can afford to hand-pick. That leaves innovation...so again we wait.