Without competition Intel can delay Nehalem very easily without causing problems for their investors. Penryn can easily be clocked up by intel with very little effort since it runs so cool, thus keeping consumers buying. After all, what else are they gonna get?
Also, when looking at the roadmap, Intels chips seem to have been getting released later in the year, each year. This seems like the perfect storm to cause the delay to 2009. Penryn is just out of the gate, has no competition, the chip is easily clocked higher, and Nehalem is a completely new architecture, which should cause more delays than any of the previous chips that have been released in the past few years. I highly doubt we will see Nehalem in any computers this year, and certainly not any Macs. I certainly wouldn't mind being wrong however.