Why bother being warm-blooded?

This article goes through several iterations of reasoning as to why warm-bloodedness might be useful. It's so interesting, I can't believe that people might just say "don't bother asking - God did it". Even if God did do it, why split cold- and warm-blooded animals? Invoking God doesn't answer anything.

http://www.newscientist.com/article/mg20126942.000-whats-the-point-of-being-warmblooded.html?full=true