Well that's exactly what i meant. One needs information from the book to know where the link is in the other dimension. When this information isn't accessible we got a problem. Nether Portals and Twilight Portals aren't that useful for RoC power transmission imo as we have nearly no control over where they link to.
Using a vanilla Nether portal for example would still require a huge amount of shafts and other tools to transfer the power several thousand blocks. This would be no improvement to the current state imo.
That only works for vanilla Nether portals and TwilightForest portals afaik. And the first one isn't a huge improvement over the current situation(see comment above).
With mystcraft for example one can link coords x1,z1,y1 in dim X to coords x2,z2,y2 in dim Y through books. The book is then placed in a crystal portal. But nothing guarantees that a portal on the other end exists. It could be a one way link or the portal back could be just 20 blocks away from the coords x2,z2,y2 portal_1 in dim X links to. These coords can have several thousand blocks on the XZ plane from each other. Thus checking coords x1,z1,y1 in dim Y could return no portal blocks at the given coords.
Now of course if the portal mod includes an API which gives you the coords x2,z2,y2 all is ok.