I haven't dug that deep into the tC specifically, but the first cat is usually a two way and the second is a three way. The reason is to get the first one lit as soon as possible after start up. You'd be amazed what the OEMs do to meet cold cycle emissions, it's a huge effort.
Yeah, I should probably pull out the books and confirm the location of the second O2. Here's the other part though, the first one is usually smaller and the more restrictive of the two, at least it is that way with Supras.