I think I.F. made a broad shift in their product line because I agree with you on the oldies being naturally vented. You don't see their advertising hardly at all anymore but then again, they seem to be focusing more on commercial than residential, which is totally different marketing.
Back to the focus of my original point I would like to reiterate that inspite of ANY mfrs. claims, I prefer going by what my instruments are telling me rather than their propaganda.
Another problem is, there are devices and gizmos for sale that generate positive vent pressure and are being sold to a market who are lead to believe it is ok with traditional galv. pipe. Some even say to goop the joints with red RTV out of a guilty conscience, such as most pellet stove venting. All pellet stove venting in the US is technically illegal. I'm working on changing that.