Exactly right. The thin plates are there to allow the manufacturer to stack more of them in the space. More plates = more surface area = more possible current (starting current or CCA, cold cranking amps) Starting batteries are optimized for short, high current discharges followed by short (relative) high current charges, as you would find starting an engine.
Can you use a deep discharge, yes, should you, probably not. If sufficient current is not available to the starter then the starter speed will be reduced causing harder starting. Compounding this the voltage available to the engine will also be less and if itís a gasoline engine, harder starting (Iím not sure about diesels, never having worked on one).
Using a deep cycle battery for starting is as wrong as using starting batteries in your house bank.
There are two types of fools...
One says this is old, and therefore good..
The other says this is new, and therefore better...