It's possible the next revision (around christmas maybe?) will have meroms in the 15" and 17" and a low power dual core yonah in the 12"/13".
I'm actually thinking apple should make macbooks in two configs:
11" Widescreen Ultra portable -$1200 - $1400 AU (Current 12" is $1600AU)
13" Widescreen Ultra portable -$1600 - $1800
Both with low-power dual core yonahs
Then macbook pros in two configs:
15" Widescreen
17" Widescreen
Both with Merom chips
That way apple are still handling the 4 screens, but there are less "pb or ib???" threads and less confusion. The only difference being processors (And possibly gfx cards) could work.