IMO Dungeon Finder is not necessary so long as the servers can maintain an active population large enough where trying to farm HC's is limited to peak hours and even then you're lucky to get one or two done before someone has to leave.
Besides not including it at launch gives Blizz the option of adding it in later when ICC phase begins, like how it was BACK IN THE DAY.
I dont give a hoot about "BuT MUh CoMmUNIty" if it means I'm stuck on a dead realm where my ability to play the game is crippled by lack of population.
And dont even start with the "BuT JUsT MiGRaTe tO a HigHEr PoP ReAlM" argument. It didnt work back in the day and is sure as hell wont work now.