From a marketing POV I guess it makes sense. You have Nissan, GM, etal increasing range. So 200-250 mile range EV's for half of what you are charging for your base model. *CHOP, no longer a marketing problem.
Seems unnecessary to me. Ideally for a consumer... range should be a separate option from luxury, acceleration, utility, style whatever else. But I guess in marketing product things are not always done in an ideal way. Unfortunate. Hopefully the base 3 doesn't end getting chopped.
The reasoning to drop the 75kWh models from the S and X probably have more to do with:
1. Separating them further from the Model 3 and
2. Morph the model nomenclature to the current naming theme of range vs. size of battery, i.e. short, medium and long range.
They will probably introduce a new lineup/refresh of the premium lines as the 2170 cells are brought into the S and X lineup that will have a long range and extra long range as Musk inadvertently let slip during his China ground breaking ceremony a few days ago.
Only the Model 3 and eventually Model Y, would most likely have a short range version.
I would expect a 120kWh battery and 400 miles on the next major updates for those two models as possibly the extra long range and the 100kW to be the long range.