Attached is a screen shot. Note that on the browse/server pane it says "1 album with 27 songs by 2 artists".  I have the "artist" tag set as "Bach" and the "album artist" set as "Gardiner" for ALL tracks.

I've tested this on several albums both single-disc and multi-disc works with various combinations of these 2 tags set.  My conclusion is that when the "album artist" tag is blank, SS shows "1 artist" in the browse/server pane; however, if the "album artist" tag has anything in it, SS shows 2 artists.

Seems like that is an error.  The info line in the browse/server pane ought to simply say "1 album with 27 songs by 1 artists" when each track in the album has the same artist.  This should be so regardless of the content of the "album artist".  My conclusion would be so for classical at least since I would think most folks use the "album artist" to house the orchestra, or conductor, or something like that.  Perhaps the arguments for pop would be different.