It seems that viper was curious as to why,

when uploading photos they suffer a major quality loss

... and so, I took a second look. 

The first image in the gallery (garden tub_001) has the dimensions
462 x 640 -- that's about 300k pixels ... and as an uncompressed image
would be a file of about 887k bytes.  However, the image in the gallery is
actually a compressed JPG with file size of 25k (25,242, to be exact).  That
image has been compressed to only 2.8% of the original file size. 

The question would then be how (when) did that happen? 

We need to know ...

(1) what was the image file size as recorded by the camera?
i.e. the original file size of the image?

(2) what was the image file size after being edited (Photoshop or whatever)?

(3) Are there any other processing steps?

(4) did MS live do some "innocent" editing of the images before
or as part of the upload process?  e.g., does it create a local copy
of what it is going to upload -- what are those image file sizes?

That detailed inspection of the work process would shed some light
on your mystery. 

--
Martin

p.s. "shed some light" -- geeeee, it's like taking a picture.  LOL