There is no reason for sadness my friends. No reason at all.
Remember the development order for the original series of games
EU --> HoI ---> Victoria ---> CK
I still remain fully confident that in the fullness of time, Paradox will develop games that will cover the time periods Victoria and CK currently cover, and the experience in developing HoI3 will only serve to make future 19th C and Medieval titles developed by Paradox all the better.
So, rather than pining away for what might have been with a new 19th C or Medieval title being developed now, embrace the news of HoI3 being developed, because what we will likely see during the development process of HoI3 are gameplay elements that likely will find their way into future titles.