Photoshop not presenting alpha channel as expected (like I'm seeing GIMP does)

Question

Greetings,
I have a need to edit the channels independently (the values in my image mean things numerically rather than just what it looks like visually - so I need to edit the grayscale values in each of the R - G - B - and A channels seperately).
I've searched through google and other forum posts and others bring up the concept of not understanding alpha versus transparency - but I have yet to see an explanation that fully explains what I'm experiencing.
The closest was http://forums.adobe.com/message/2563436#2563436 But while I saw the exact same symptoms being described, the specific question was never really answered.
Hopefully, a concrete example with pictures will be able to communicate the issue and solicit a useful explanation and/or solution.
While, I'm specifically working with an RGBA image, below is a screenshot of a PNG that demonstrates the exact same behavior or symptom.  The screenshot below represents the PNG inside GIMP and PS CS4.  BTW, if you'd like to see or play with the image yourself, you can grab the same image at http://www.libpng.org/pub/png/img_png/imgcomp-440x330.png
GIMP, interestingly enough loads the PNG as expected - I see the transparency of the image treated as a true alpha channel.
In PS CS4 however, the transparency seems to be somehow embedded in the Red - Green - and Blue channels; but NO seperate alpha channel.
I can create the alpha channel through Select - Load Selection - Layer 0 Transparency - and pasting that into a newly created alpha channel - but the color channels still have the transparency mixture symptom - rather than showing the JUST the color component of that channel.  (Note the channel differences of the GIMP's Red Channel versus PS's Red Channel  - Said in another way, the yellow ball in the upper left of the image should have a red value of 255, so the Red Channels grayscale upper left ball should be white like it is in GIMP, rather than Gray as it is in PS).
I never thought I'd experience GIMP being superior to Photoshop - so hopefully somebody can shed light on what is going on - what configuration I may have myself in - or a process to get the channels seperated out in the manner I wish to work with them.   Furthermore, maybe somebody can educate the Photoshop community what the difference between transparency and alpha[transparency] is.  I haven't found quite the right explanation that makes the light go off in my head yet.  As best as I have gleened "Alpha", which can be applied to any kind of channel, typically is in reference to transparency - and is applied as a document-whole transparency (as opposed to transparencies applied at a layer level - such as a layer mask).

Answer 1

I think I've finally determined that modern Photoshops have gone in a different direction that I feel "Alpha" should be done.
(good or bad).
Here are the steps and/or details of how I arrived at that conclusion.
If nothing else this has been very educational on how Photoshop treats alpha.
- Import your alpha'd PNG with SuperPNG format (see above on how to make sure you use the SuperPNG plugin to load the .png).
- In the SuperPNG dialog select "Alpha appears as seperate channel"
- Create a layer from the Background and Delete the original Background
  (since the Background is locked and we can't edit the Background - we want to add a layer mask based on the alpha)
- Ctrl-Left Select the "Alpha 1" channel - Ctrl-C - and hit the "Add Layer Mask" button (square with the circle at the bottom of the LAYERS rollout)
- For this demo and clarity, I went ahead and deleted the alpha "Alpha 1" that came in through the SuperPNG plugin
So now I have the Layers like I kindof expected the main document to just come in as (kindof though - it is presented in a Layer Mask rather than Alpha Channel).
What is interesting - which you'll see if you toggle the layer mask on and off
(shift-click the mask thumbnail in the layer)
Note how the thumbnails in the channel views render differently during the toggle.
When the mask is off you see the individual color channels like I expect - black where there is an absence of that color.
However when you enable the layer mask - the individual color channels show in semi-transparent/checkerboard.
So this is exactly how the color channels are presented when loading in a .png (WITHOUT the SuperPNG plugin) or an .rgba
..you get the semitransparent views of the color channels - BUT the difference is - you have no way to directly see or edit the Alpha channel.
nor are the color channels represented as completely opaque versions.
What is really interesting - it is there though - if you Ctrl-Left Select the layer, Ctrl-C, and "Add Channel Mask" - you'll get the Alpha mask.
HOWEVER, the big issue is that you can't toggle or edit the Color-Channels like the Layer counterpart above;
they are ALWAYS the semitransparent/checkboard version;  AND now we basically are double applying transparency
  (due to the still embedded alpha/transparency AND the newly create "Alpha 1" channel)
I think this a bug (or a poor reimplementation of modern Photoshop releases; I believe older Photoshops used to break out Alpha in the "arguably correct" way - and in fact the way GIMP currently does).
Or maybe there are other explanations - like abstracting some of this complexity away from less advance users, etc?
So the SuperPNG plugin was useful in experimenting, understanding, and demonstrating what is going on.
However, if I'm trying to read in .rgba directly, I don't think I have a way of making the "Alpha appear as a seperate channel" as I think any image with "alpha" component should.
(png, tiff, rgba, etc).