The amp limitation of a VV/VW regulated mod is there for safety reasons. The processor is designed to put out only so much wattage, otherwise it could sustain internal damage. The majority of regulated mods currently on the market will be able to put out plenty of wattage for the vast majority of vapers. Of course there will always be a minority who want "more power".
Voltage and wattage work interdependently according to Ohm's law. Changing the voltage will change the wattage, and vice versa. On a VV/VW mod, you can only be in one mode at a time - either variable voltage mode or variable wattage mode. Both will get you to the same place, they just take different routes to get you there.
The following chart may help you understand the relationship between ohms (resistance), voltage, and wattage.
Amps is important with batteries, also. Especially if using extremely low resistance
coils (sub-ohm). Using a coil which will pull more current (amps) than the battery actually has in reserve can cause that battery to self-destruct in thermal runaway.
