Here's your answer (you can skip to paragraph 5). Fact is, dropping certain spark plugs from the lineup is a cost-cutting decision made by a manager, not a technical decision made by an engineer. Single-platinum plugs will work, but you'll have to change them more often. I know this for a fact from experience, and there are many others more qualified than me who will say the same.
Edit: removed some redundancy in regards to my first post
