The crux of the matter as I see it comes down to 'Why?'. Why make the changes? It seems to me that all It software companies and website owners have this mania for "flex fingers" 'freshening up their design'. They have departments full of developers and at the top some marketing types who need to justify their existence. So they have to have Change. Whether the Change is for the good or not is often a moot point. In the case of iTunes 12 I see little on the web to suggest that people are happy with the Change.
Change has to be for the better. New features, for example. Not, as in the case of iTunes 12, Change for Change's sake.
Same goes for the tweaks in Mavericks. For example, I liked the little spinny thing when Mail was Getting Mail. It reassured me that Mail was doing something. I liked the little black dot inside the red dot at the top LH corner of the screen in Text that reminded me I'd not saved the document. Yes, I know it reminds me to do said Save if I attempt to close the document but somehow it just seems clunkier. Change for Change sake.
In Safari, I struggle to see if there is a valid Show the Previous Page. The differential between there being one and not being one is, to my eyes, non-existent. Change for Changes sake.
I struggle to see in the Dock whether a program is running or not. Again, Change for Changes sake.
Google are just as bad. They used to have a useful sidebar with additional search options where you could, in one click, select a date range or a country but now that is all hidden...it steals my time.
There is an old adage....if it ain't bust then don't fix it. Apple and Google (and others) would do well to remember that.