I just used VW as an example. I could have chosen BMW, MERCEDES, or BRIGGS & STRATTON.Then the odds are you've not had an engine that called for a stringent spec. If you read my earlier post you'd note that VW had serious problems with dealers in North America going by the grade on the bottle and not the spec, because, much like you are doing here, these folks thought that "oil is oil" and that if it said 5w-30 then it would be appropriate. This led to sludge and engine failure when run at the specified drain interval.
So far 5W20, 5W30 has been "OIL IS OIL" to me. My trucks engine has 159K miles on it and it hasn't blown up or even jumped out from the engine bay. I must be doing something right, by just choosing 5W20, 5W30.