Spoken like a true parts counter person. only some of what you say is right.
If a person wants to run a colder plug in their car then they should do so, it is not going to have any adverse affects on the engine. If you run a stock plug in a car with nitrous then the plug could melt the first time the No2 is used. Also, Plug manufacturer is a consumer choice, Albeit a stock engine usually works best with oem reccomended parts, I have found that alot of vehicles work very well with bosch or ngk platinum plugs. I don't want to go into internal combustion 101, but alot of vehicles leave much room for improvement in the ignition system. The only reason the vehicle manufacturer didn;t do it was cost effectiveness. Alot of companies will use a cheaper part just to keep the cost of the vehicle manufacturing down. You may not think that is true, but if you are going to produce 1 million vehicles that year and you have a coice between a 1 dollar plug and a 2 dollar plug, multiply that number by the number of cylinders, and then multiply it by 1 million, if it was a 4 clyinder car you are talking 4 million dollars for just a 1 dollar increase for a better spark plug. Just look at alot of manufacturers common problems (ford ball joints, gm intake manifold gaskets, chrysler water pumps, etc. etc.) if they put in a better part to start with no one would have the problems to begin with, but the manufacturer would have had to spen alot more money to correct the problem before it became a problem.
I would say do your research before choosing a spark plug for your application choosing a spark plug just by brand can cause detonation and spark plug or even engine failure. I'm sure Zex put alot of engineering into their plugs and reccomended them for a No2 applicaiton for a reason. They want you as a return customer, not just a person who bought somethign that is wrong.