Regardless of the weather - winters or summers, the operating temperature of an engine would be the same (this is what I think). So what is the whole fun in boggling our minds deciding upon which engine oil to use? I know that on a cold winter morning, engine oil would be viscous and it would take some "warm-up" time to become runny for smooth operation of engine, but once the engine oil is warmed up it does not depend on the climate anymore. So, are the engine oil grades (the W part of it) only important for engines in cold weather? But again, engine would become warmed up in a matter or 2 to 3 minutes; after warm up engine would be supplied with delicious :P, runny engine oil. Moreover, given that an engine's operating temperature stays the same, we can use a single-grade oil for all seasons.
I think the only thing to look for in an engine oil is weather it is capable of handling the engine when it is at its peak operating temperature which is somewhere between 160 ?C to 315 ?C (source: Wikipedia: Motor Oil - 3rd paragraph under "Use" heading).
I am confused. What is this all about? Please explain.