When you miniaturize, you PAY for the engineering required to make stuff smaller. That takes a lot of work, and hence money. Ultra-portable PCs are much more expensive than their larger, more full-featured brothers. This has always been the case.
Then clearly you're not in the market for an ultra-portable, a family of machines that have ALWAYS been (and always will be) less powerful and more expensive.
You're right that ultra-portables are almost always less powerful, and more expensive. But you're wrong to assume it will always be this way, at least from an expense standpoint. Companies like Asus, Acer, and Via, among others, are leading the charge for extremely small and extremely inexpensive computers.
Times are changing. You no longer have to sell off your first born to get into an ultra-portable machine.