They may be in different market categories, but they solve precisely the same transportation problem,
Roughly speaking, perhaps. You're forgetting the luxury and performance parts I think. The performance of Teslas are quite insane in short races - they peak quickly, but they reach that peak insanely fast. Stuff like beating a race car while towing said race car:
(okay, so it's a Tesla model X, not a S)
The S 90D w/ 19" rims (not sure precisely where that stands in the Tesla lineup)
It's their premium non-performance car. The 90 means that it has a 90kWh battery, and the lack of a "P" means that it's not a performance edition, which is a little less efficient, but much more powerful. The D means that it's all wheel drive.
They're getting ready to come out with 100kWh batteries, which would be designated with model numbers like "S 100D", "S P100D"
The reason why the S70 would take longer is that the 70kWh battery isn't capable of taking a charge as quickly as a 90. Also, if I remember right, it only has half the internal chargers of the 85 and up models, which also limits the speed at which it can charge.
Eh, here's the ultimate deal, I think: Tesla has developed battery swap technology where you drive over the system and it swaps your battery for a fully charged unit(and can put a larger battery on to boot, so it can take off a 70kWh battery and put in a 90kWh one for your long drive), in ~90 seconds. However, among actual owners not enough interest has materialized to get Tesla to install them. They'd prefer to use the free superchargers than pay for a battery swap.
My uses for a car are infrequent trips to places nearby (Dr, dentist, etc) and long road trips,
That's fine. Not everybody takes long road trips.