Finder: "Devices" vs. "Places." Why are the programs different?

Question

I'm perpetually perplexed by the way the the same applications work differently under "Devices" and under "Places" when accessed from the "Finder." For example, often when I access a program like iPhoto from the Finder and click on it, it will appear to the extreme right on my dock, next to the stacks divider, thereby giving me 2 icons of iPhoto on my dock. Moreover, the one that appears on the far right may be of a different size and behave like a program being used for the first time. At other times, accessing the program from the Finder merely opens the one program on my Dock, as I expect it to. But must there be two appearances of the same icon, each appearing to be a discrete, separate application (as I suspect they are) rather than a mere alias of, or short cut to, the same program?
A most recent example: I downloaded iTunes 10 (twice, for good measure). Nevertheless, I'm now looking at two different iTunes programs: iTunes 10 is under 2 of the rubrics in the "Devices" area of my Finder ("my iMac" and "Macintosh HD"); iTunes 9 remains lower down under 2 rubrics in the "Places" area (under "Applications" and under "my name" as sole user of the computer). They clearly must be separate, discrete applications, with different file sizes, though I would prefer to have only iTunes 10--and located under "A Applications" in the "Places" area of the Finder window.
Normally, I would access applications under the "Applications" rubric that's found in "Places" on my Finder. Doing so, however, would seem to require that I trash my old iTunes (or iPhoto) and replace it by dragging down the newer version of iTunes recently installed in the "Devices" area of the Finder. Is this normal procedure? I plan to make less use of the Finder and concentrate on what's in the Dock. But when dragging an application to the Dock, is it important to select the application from the Devices area ("Macintosh HD") rather than the "Places" area ("Applications") to ensure placing the most recent version on the Dock? And is it normal to see two versions of the same application appear on the Dock after clicking on the program in the "Devices" area and the "Places" area of the Finder window?
I'm analytically-challenged but am looking to reduce clutter without inadvertently trashing what may be substantial. I could also use any enlightenment concerning the complex and multiple locations (apparently 4) of a program/application as seen from the Finder window.

Answer 1

I'm perpetually perplexed by the way the the same applications work differently under "Devices" and under "Places" when accessed from the "Finder." For example, often when I access a program like iPhoto from the Finder and click on it, it will appear to the extreme right on my dock, next to the stacks divider, thereby giving me 2 icons of iPhoto on my dock
Sounds like you have 2 copies of iPhoto installed.
On the dock icon, right click -> show in Finder and see where the applications are located then delete one of them
Drag iTunes 9 to the trash to delete it.