Mac programmers did not have much time to adopt the new platform. Apple originally targeted June 2006 (or at least they said so). Moving the code to the new system is easy for some, but hard for others. It will take time, nevertheless, before the signifikant amount of programs runs without let or hindrance. Until then it’s just the power users, chronic early adopters and the programmers who will flock to the new machines. So there is a reason that the MacBook is built the way it is: it attracts primarily programmers.
The machine lacks a lot that creative professionals need. VJs for instance can’t really use that machine at all. But their software will probably take long to arrive anyway so it doesn’t really matter. They wouldn’t switch now anyway. So they go for the PowerBook for the time being.
The programmers however will like it: it’s got all the necessary networking, basic USB and FireWire support and it has brand new stuff as well: the ExpressCard slot directly targets developers – software and hardware developers alike.