It's not the same thing actually... Core Duo used in MBPs was Yonah based and it was 32-bit and had only 2MB of L2 cache. Core 2 Duo was Merom based (Penryn based at the moment) and it was 64-bit and had bigger L2 caches. The difference between those two is huge.
Arrandale is Nehalem based and there now be new architecture before late 2010 but more likely 2011 when Sandy Bridge comes out. Clarksfield might go 32nm in mid 2010 so that's the next CPUs we can hope for MBPs after Arrandale. I'm not sure is Intel planning to release any other quad core 32nm mobile CPUs in 2010 but I hope they do