"They want developers to start making Longhorn apps now, so that 3 years down the road, there are Longhorn optimized software out there as an incentive forthe public to buy it. "
To which I imagine developers to reply "No thank you." Why would you develop something now, or start doing so, so that a year or two later (a year or two given for development time, of course,) you can release something? Would any software house want to sit on something for that long?
They can develop something and sit on it, or develop something and sell it now? Nah.
Besides, hopefully, by the time Longhorn gets released, 32 bit architecture will be all but dead. That is of course, if you can convince AMD and Intel to drop their 32 bit offerings (and have them be able to make 64 bit affordably,) before then.