There must be something else to it other than plain old price gouging. 28awg is the only ss316 temco wire that isn't cheap.
I'll be honest I really don't know. I'm not seeing an immediate difference between them when I checked last night. That's not to say there isn't one between the two wires that wasn't immediately obvious to me, but it's no promise there is one either.
Temco is a good brand in general, and it may be attributed to something as simple as trying to dissuade vapers from using their wire, 28 gauge being one of the most popular sizes for coil building.
Sony tried hard for a while to stop vapers from using their batteries because they didn't want it to be their name in the news when someone did something stupid.
I'm far from stating this is the case with Temco Industrial, but it wouldn't surprise me either.
What you may like to do, is call Temco customer service up and simply ask. I never knew there even was a price difference until you pointed it out, so it certainly wouldn't hurt to give a call and just ask.