Often, a comparator or op-amp model has the output clamped to a reasonable range. And, yes, I've seen models for e.g. LM339 where the output is active driven the whole way, as if a decomp LM358.
Manufacturers don't like using complete transistor-level models for a few reasons:
1. Hiding IP.
2. It runs faster (maybe, unless convergence errors screw it up worse).
3. If we can make one, and adjust the parameters to fit most of our product line, we don't have to waste time dicking around with more models. (Hence, comparators sometimes lacking faithful open-collector outputs..)
Even in the olden days, when they provided equivalent circuits, they didn't say what kind of transistors were used, nor how large. There are a couple tricks in monolithic design that can't be reproduced easily in SPICE, nor expressed easily on a schematic (which is part of the reason you see confusing things like transistors having multiple emitters or collectors: it doesn't make sense from working with discretes, but it makes a lot of sense on the monolithic level).
MOS capacitors are notable, because unlike metallic capacitors, the capacitance varies with voltage (it's a MOSFET gate, sans FET). These are commonly used for compensation, so expect the fT and gain to vary with supply voltage and temperature. Canceling out these effects is a tricky part of design, and may be easily missed in a transistor-level model; even being able to measure the effects, and adjust the parameters to match results to poorly-documented datasheet parameters (like gain and fT vs. VCC and TEMP, if they provide any of these at all), is tricky.
Obviously(?), such fine detail is normally missed, or just approximated, in a behavioral model. But it's up to the model designer to determine if that's good enough or not.
And so, you often have the case where the output voltage is a fixed Thevenin source (often with a current limiting circuit as well), and so doesn't behave like a real device where the output can be pulled closer to a rail using a resistor or CCS.
This goes for most digital sims of TTL logic too, I think.
Tim