As far as I know it isn't possible to get an 80GB drive for less than a 40GB drive, but I do know for a fact that at consumer prices, a 40GB laptop drive costs less than $5 less than an 80GB laptop drive.
Sub 100GB drives vary so little in price that you really can't save a substantial amount of money by swapping one for a smaller drive. Even if they created a model without a hard drive, they'd save less than $45 (and that's assuming they pay consumer prices, which they don't).
I don't doubt that Sony is preparing a new model. But believing that they can save $100 by reducing the size of the hard drive is retarded. A memory stick reader costs $10 at consumer prices, so it's not like taking that off is going to result in a $400 model either.
The reason the PS3 costs what it does is because of the Cell processor, Bluray drive and to a lesser extent the RSX. Adjustments to any other components will result in a minor cost reduction at best.
