I think you need to take a step back from how you've been thinking up to this point and ask yourself: How do (semi)immobile machines contribute to gameplay?
It's not about gameplay.. it's about realism. In REAL industry, machines that are too large to practically be moved are assembled on-site, due to their volume and sheer complexity. The reactor itself may look like 7 blocks to you, but 3-by-3 meter^2 device that usually weights alot more in a plant's core than Minecraft is showing.
Industrialcraft (thankfully) goes for realism instead of immersion. It gives examples of real-life aspects that occur in the world of industry, and we as players have to tackle them in our simulated world. Because of this, we are given the same limitations that we would encounter if we were to, say, pursue a career in electrical engineering or energy management (to a degree. I still think Pollution should be a troublesome aspect of the game, lol). In which case, the mod itself becomes a teaching tool for those of us who do have interests in these types of careers, or are already involved in said careers anyway. This way we can relate more with the fictional 16 bit world that is Minecraft in a more relative form of immersion from what we experience beyond just 'gameplay mechanics' for fictional machine blocks...
Quite frankly, if this mod didn't have that sense of realism, I doubt so many people would play it.