They are sort of, but assembled into packs that are larger and bolted together to maximize space and reduce wiring. If you remove the seats and some covers they are relatively easy to get out most times, but they are still high voltage and can easily harm you if you aren't careful.

There is not much difference between the battery cells and the ones in drill batteries, but if you needed 100 drill batteries to use your car the packaging would take up lot of space, and then you would need more wiring because you have wiring inside the drill batteries and wiring to get the batteries from the receptacle to the rest of the vehicle.

The battery packs last long enough that making them difficult to get out isn't an issue. You can service individual cells or groups of cells, but getting an entire refurbished unit is recommended because if ones going bad you may end up fixing more not long after.