After two chat session, three phone sessions and a visit to the Apple Store (where I found a blue shirt who was a photographer and was just as confused as me - we spent over an hour experimenting and this is what we discovered - remember I'm a Windows guy - we played with a Mac and my Windows laptop in an attempt to figure out what's going on.
1. iCloud Photos is not a backup (surprise surprise) it is a sync system. - if you delete a picture from your phone or iPad - it is deleted from iCloud.
2. iCloud Photos does have full resolution photos in the cloud.
3. If you download a photo from iCloud.com to a Mac or a PC - you are given a lower resolution file (Shared or not shared photo/album makes no difference)
4. If you email a photo from your iPhone you can send the full resolution file (or you can choose a lower resolution)
5. We were able to get a full resolution file on the Mac by obtaining the photo thru the Photos Application on the Mac to iCloud.
That appears to be the only way you can get full resolution photos from iCloud.com
There appears to be no way to get same from iColud.com with a Windows PC.
6. My Photo Stream
Have discovered the iCloud desktop application for Windows - which appears to put the full resolution files from iCloud.com onto my PC - but not consistently. Will have to do some further reading.
We looked and searched every where in the Apple help for some document that addresses the downloads one gets from iCloud.com - nothing. . .same thing the "Lead Engineer" on phone yesterday found - nothing.
For now - I'll just email myself the full resolution pictures that I want to edit on my Windows PC with Photoshop.
Will head over to Lynda.com and see what they - should have started there.... ;-]