Programmer - Using InvariantCultureIgnoreCase instead of ToUpper for case-insensitive string comparisons

On this page, a commenter writes:

Do NOT ever use .ToUpper to insure comparing strings is case-insensitive.

Instead of this:

type.Name.ToUpper() == (controllerName.ToUpper() + "Controller".ToUpper())) 

Do this:

type.Name.Equals(controllerName + "Controller", 
     StringComparison.InvariantCultureIgnoreCase)

Why is this way preferred?