Technically [rust][1] is limited to iron. What is bad is the rust starts and continues. The water / oxidizing agent is not consumed. Aluminum will oxidize but it forms a protective coating. An aluminum frame will not "oxidize out". Some iron alloys such as [stainless steel][2] prevent rust. I don't know why you don't seem to see stainless in bicycles. [1]: https://en.wikipedia.org/wiki/Rust [2]: https://en.wikipedia.org/wiki/Stainless_steel