If Adobe redesigned the Photoshop interface they'd instantly love half their market share, as people using software professionally don't like or have the time to learn something new just because it's better in some odd way.
Microsoft did that with Office, the whole Ribbon fiasco, but to their defense: - Office 2003's UI was extremely complicated; GMail's new extra steps are nothing in comparison. - The Ribbon UI was well designed from the start. - All (or most) keyboard shortcuts stayed the same. - Microsoft actually did extensively test the new design and, being Microsoft, it will be supported for a long time.
Adobe probably wouldn't be able to pull that off, and it looks like even Google can't anymore.