Yes the batteries are different, i don't know if the lead acids are not used because it is old tech. Thought the problem with lead acids is more along the lines of heavy tech. Pasted plate starting batteries are not made to be cycled to any depth, deep cycles makes the paste fall off the plates. Makes the battery fail quickly. Good deep cycle batteries, forklift batteries, will handle years of cycles before needing replacement. But a small forklift battery weights half as much as my car. And the heavier the car is the less fuel efficient the car is as a rule. But if hybrids used lead acid batteries i might have more faith in the long term viability of the car. The problem i see down the road, other than the replacement cost of a new battery, is when the car is 10 to 15 years old the battery fails and you go to the dealer and ask for a new battery. And they smile and say we don't make that part anymore. You now have a nice hybrid boat anchor.

You are also correct, if the maker still has the battery years down the road it will cost more than the car is worth for replacement and installation.