The game mechanic called "fast travel" (that I also like in that kind of "open world" map) exist in many games in which there are no teleportation portals... It has nothing to do with concession, it has to do with the choice they made to design the system arround "not lore" magical portals. This is one exemple among many others in which they could have made a better representation of the world without even changing the mechanics at all. .
I get your point... I even agree.. Magic Portals are in and of themself lore based but the all over the place nature is not. Looks like they took a minor lore function (seen them used in many books but for very specific locations) and then thought what a cool idea and just used them for fast travel. Your right however, I think use of road signs would have worked just as well and even been better but even that does not work as some of the locations would not have had road signs. They wanted an all in one type solution and this is what they chose.
