I don't agree that the auto save is for text and not images. Keynote is auto-saving. My Pages documents are auto-saving. Preview files are auto-saving. Even my TextEdit files with images inserted are autosaving.
The way Adobe documents behave and the way Adobe chooses to give its users the SAVE AS option is not so much a reflection of the document content as it is Adobe's realization of the way people work.
This is a critical point in the understanding - and misunderstanding - of this issue.
One might say that working in Adobe's creative suite is more of a "creative process" than working in Apple's iWork suite of applications, but I think Steve Jobs and Phil Schiller would have quickly denied that whenever they did their wonderful demos showing the creativity users can apply to their iWork documents.
In the creative process, we don't necessarily want to save our work until we are ready to do so. Because of the size of certain images, doing so in a program like Photoshop with a large file open can result in a huge waste of storage space. If Apple was thinking clearly, they could have come to the same realization about Keynote and Pages files that contain media, even if Numbers files are strictly alpha-numeric.
Photoshop users are familiar with a command called Duplicate, in which a new window opens with an identical array of pixels, allowing users to edit and design as they wish, and committing the new window's contents to a file stored on disk only when the user desires to do so.
So, if Adobe now realizes that its users might like to benefit from Apple's new technique of auto-saving they have enabled the feature in a way that allows the user to decide. If I am working with a 200mb photograph, I should be the one to decide whether I want numerous auto-saved versions on my hard drive -- or worse yet, on my expensive solid state drive, or do I only want to have saved editions of the ones that I really care about being able to compare. Otherwise, if you have dozens of versions in your timeline and you want to revert to a particular one, how can you differentiate them? Adobe files with layers and channels and delicate color adjustments are not as easy to differentiate as an iWork file which has only 1 layer and and alsmost always containts text that very easily differentiates each auto-saved edition.