Yes you are right but that is specifically due to the drawbacks of a typical 4-stroke gas engine running on liquid fuel. Heat is needed to vaporize and mix the fuel and air before it's burned especially in carb'd engines. If it is possible to get the fuel completely vaporized and mixed with the air inside the cylinder without using any heat you will have a much more efficient and clean-burning engine. That's why I mentioned the HCCI, in theory it uses no spark plug and compared to conventional engines has a very cold combustion with rapid but controlled burn. Basically in one of those engines the mixture is compressed to where it auto-ignites but the ignition doesn't start at one "point" (spark plug, or injector tip in a diesel), the entire mixture lights off simultaneously.
As you can probably guess the main problem with its application right now is how to control it since there is no device to initiate the combustion process and we all know how tricky and persistent uncontrolled detonation can be when you're pushing the envelope... Really tough to not make things go BOOM