Quote from PathologicPC version didn't have offline to avoid potential security issues which don't exist in a console version. PC will not get offline mode - don't get your hopes up.
To begin with, Blizzard has said nothing about cutting online requirement, if you have anything on that, share source.
If they however do indeed provide an offline solution, I for one will be very happy as that will open up for exploring how the game works. In the end that could lead to hosting your own servers and modding the game!
As for the true reasons as to why we have online only, my guess is security through obscurity but foremost for the control they regain over their service. Just look at SC2 how they moved hosting of maps towards bnet away from the players, something that lets them control user content way more. I miss the strip poker maps