Your point seems to be that all zombie-human interactions will, at all times, happen in a completely controlled and crafted environment in which the deck is stacked 100% in favor of the hardened, emplaced, well supplied, well coordinated, humans.
MacArthurian thinking at its worst, really.
Ain't gonna happen, as reality (and a zombie) has a way of popping up and biting you in the ass when you least expect it.
Lord, don't you love how passionate we get about topics that are complete and total mythmaking?
I actually think it's totally uncontrolled. The whole point is a strategy that requires minimal people to control an extremely large area with minimal resources, and as more resources become available, expand that to eliminate the threat.
The whole point about water towers is (and also why they are never used in movies):
1. They are tall
2. They have limited access (single ladder usually, easy to remove/block)
3. Other than the ladder, they have nearly impossible to climb supports
4. THEY ARE FULL OF WATER--by far the heaviest and yet most needed supply
5. Their catwalk enables a simple lean-to to be constructed
6. Height enables drawing z from far away
7. Two within mutual sound of shot range means leapfrog back-and-forth strategy is possible
8. They are fire resistant meaning "set fire to Zeds at the base" is, while normally a bad tactic, actually a reasonable one.
9. Large top-area means lots of space to lay out solar panels w/ zero shade and optimum angles
10. Height enables easy and efficient installation of wind generator
11. Helo's can land on them
12. Height improves radio and observation range.
Anyway, macarthurian is a bit harsh.