If the speaker itself is already rolling off in the vicinity of the crossover point, then it's slope is added to that of the crossover. If the speaker's natural rolloff occurs an octave above/below the crossover point, they are offset enough so that addition does not take place - there is minimal interaction.

Yes, a steeper crossover does take place over less bandwidth than a crossover with a gentler slope, but nonetheless if the speaker is already rolling off in the crossover region, then it's slope is added to the total slope. A steep crossover is best if there is adequate excess bandwidth available below or above the electronic crossover point.

This is an issue because many satellite speakers simply don't have solid response down to the 40Hz that would be required for no interaction with an 80Hz crossover network.

The manufacturers really have to design for the worst case, that that worst case is the reality that many speakers are already rolling off in the vicinity of 80Hz by themselves because of their small woofers and cabinets.