You may be right in some cases. In others not so easy. If the noggins or top plates in internal walls are not punched or there is insulation it may be quite hard to get cables through. In all brick construction there are no cavities in internal walls. In external walls insulation may be a problem.
Many modern houses have quite shallow roof spaces (14 to 20 degree slope roofing) and it is very hard to get around in them at all. Out near the external walls it may be impossible. Electricians can resort to taking off part of the roof to get to the top of external walls.
It is hard to say how it will go without trying it. I would not encourage people with no experience to count on doing it sight unseen.
