My question would be a defined "Why change it?"
For what purpose would the change serve? What factor lead up to the belief that a change was needed?
So far, the success Apple has found with their products tells me two things...
1.) They are not in any situation where something like a logo change/refresh would be a necessity.
2.) They have such a visually impactful logo that a change to it MIGHT be detrimental to their success in some way.
...it's kind of like Ford and Chevy. Have they done polishing to their logos? Very slightly...but over many decades of success. Right now, Apple doesn't need to change a thing.