I will give an example of why Lion is still needed. My wife is an experienced textile designer and very long time Mac user (shameless plug: see her Hawaiian and surf-themed iPhone and iPad cases here: http://www.hawaiiancases.com). Because of Adobe's constant foot-dragging on staying current with OS-X, she has been forced to run at least one version behind the current edition of OS-X in order to assure compatibility with Photoshop and Illustrator. Only now could she feel assured of being able to upgrade to Lion, but this morning, to her surprise, she found that Lion was no longer available for purchase on the Mac App Store.
I can give at least reasons why Lion is still needed by many professional users - and my wife is desperate to purchase a copy:
1. The Fiery RIP in my wife's very expensive printer/copier just updated its firmware yesterday for - get ready - Lion. There's no telling when it will be compatible with Mountain Lion.
2. Adobe has not officially announced that either CS5 or CS6 is compatible with Mountain Lion. However, I corresponded with the ever-helpful David Pogue, who assured me that he just completed a 900 page book on Mountain Lion using Adobe products, and he was/is running Mountain Lion. That helped us breathe.
The simple fact is that a number of apps and firmware are not yet certified to run correctly with Mountain Lion, particularly specialized software/firmware that my wife uses for her work. And that makes it imperative for my wife to obtain Lion.
Apple, please help your professional users. Make Lion available again!