I believe you are correct. I would like to know why though. Even though I personally don't usually (although sometimes!!!) need amp/cab modeling, it would be great if @Digital Igloo could stop by and update us.
I think the problem I have is that users don't always fit into neat little categories. So is somebody a pedalboard person or an amp person? Depends on which day. Does that mean I have to buy two different almost-identical products? Why would a user want options left out? It's not like they take up room. If on the other hand it's a cost thing, I think most of us who want amps and cabs would be willing to pay for the extra models.
This kind of thing is one reason why a strict hierarchy of products is easier to deal with: A > B > C > D. This ecosystem doesn't have a clear relationship between Stomp and Effects. That's how it appears to me anyway.
If I was to take a complete punt at it, and I'm not an engineer here so who knows, I'd say that perhaps they've done it this way from an engineering perspective because of the amount of DSP power available in the HXFX. From my understanding, the HXFX and Stomp each have 1 DSP chip, as opposed to the 2 chips in the LT and full Helix. The HXFX has 9 blocks and more complex routing capabilities, as opposed to the Stomp which has 6. Perhaps another reason not to put amp/cabs in the HXFX is because of how quickly you'd run into the limits of the DSP, and the negative impact therefore on the full capabilities of the HXFX.
I mean, what's worse? Users complaining that a particular product offering doesn't contain something they want? In which case, they buy a different offering? (or from what I've been reading with some guys, they're buying both!)
Or users buying a product on the premise it can do something, only to find that due to hardware limits, it can't do what they want it to do? If I was the manufacturer, from a product returns perspective, I know which one I'd pick...