Hi DonM
There are very few programs these days that don’t use Dual core CPU. (Particularly Music, Photo and Video programs)
The road map for multicore processors was laid out a couple of years ago, (8 cores should be out next year, with possibly 16 core towards the end or early 2010) and so manufactures adapted their software at the same time as they moved over to Dual core. (Dual and Quad core are also starting to be used on High end Graphics cards)
In addition single core CPU is a fast dying breed.
Regards

Bill