Currently there is a city phase technology that gives all towers +2 armour. This patch changes that to +25% health instead, and renames the technology accordingly.
The effect is basically the same (1/0.9^2 = 1.234568), but it seems most people don't understand how armour works, therefore just changing health is clearer.
Technologies (including civ bonuses) are permanent, therefore them changing health is perfectly fine. (In contrast, auras (including team bonuses) are temporary, therefore those shouldn't change health, just armour, to prevent edge cases when access to an aura is lost.)
While at it, all tower production queues are updated to have all technologies that actually affect them and only those (something I forgot in D2549).