Umm...Every race has to reinforce constantly unless they're terribly far ahead, that's not really race-specific. If I start getting aggressive with a 6-7 gate push and don't have a pylon up at their base, I won't reinforce enough to deal with defenses. If in the lategame I run into a blob o' army, I'm hosed unless I recover right away, because -they're doing the same thing-. Zerg may need higher numbers, but they can also burst-replenish their army a whole heck of a lot faster anyway. And I still don't believe that the zerg can never win stand up fights ever until BL. infestors do a great job with that via fungal. Ultras are a pain in the ass unless the other side is well prepared, and unless their scouting happens at just the right time, a sudden surprise of 7 ultras that weren't there a minute ago isn't that hard to pull off.

Actually, I think that's the real zerg "hidden tech" thing. It's not hiding the building, it's that they don't need to have that building for long before it makes a huge change in their army comp. It takes forever for me to get a notable amount of...well, anything but templar tech after getting its associated tech structure. In the time it takes for me to get a robo and get, say, three immortals, that would be the equivalent of dropping a hydra den and getting, say, 21 hydras. I know, I know, "but you've also got gateways", but I can't repurpose those into getting immortals if that's what I need. It's the 2 minutes where you don't see their base or army and suddenly it's entirely different that is the zerg hidden tech.