I was once issued a helmet which had been manufactured by a company which also manufactured motorcycle helmets. The company was based in South Africa, called "Lafe" with an accent on the e. They had seen the demand and the exorbitant cost of flight helmets when the import duties had been factored in and sold a bunch to the Air Force. I found it to be extremely well made and very comfortable. They used exactly the same technology that they used for their motorcycle helmets but changed the shape of the shell to accommodate the earpieces, visors and NVG's. Unfortunately they no longer make helmets for helicopters.
I see no reason why a decent motorcycle helmet which has passed the required testing should not be used and as has been mentioned, CEPS and a microphone would be really easy to install. Motorcycle helmets are also probably more comfortable to wear for long periods since they are vented and have decent interior padding. The companies which make them have a lot more money for research than the typical flight helmet manufacturer.
I have an Alpha which I am very happy with but I would not be against having more options in the future.