To say RTS relies more on resource gathering than TBS is to oversimplify the issue.
RTS has SUCH a simple economic system, with such a powerful military system, that the strategy you just mentioned becomes extremely powerful.
TBS makes the economy more tricky. So yeah, it's not just resource gathering. But it's also challenging enough that you can't quickly bump off the source of an empire's economic strength.
(Mind you, if you've played multiplayer, you do learn quickly that "the choke" is pretty important. Even if you can't destroy someone's economic foundation, you CAN scare their worker inside their city borders, keeping them stuck for a while.)
I'm curious if you have the article in mention? Think you could find it?