Don't really know, but check out the price of 16F84A (very old but still in production) with 16F628A (pin compatible and better in every way). From my supplier the 84A is 3 times the price.
I guess they are trying to persuade people to upgrade so they can phase out the older ones someday.
Look at the 18F series, often almost as cheap and a lot of juice. For example PIC18F4550. Program in C ( free compiler from MChip ) Look at how the usb bitwacker does it, or get one.