I know exactly how you feel! It is a rare event that my little riding group overtakes and passes a fellow roadie, so when we do, we wait a respectful distance so he/she doesn't hear us, and then we definitely do a little celebrating! Of course, we usually follow that with some remarks like "well, they were probably finishing up a century ride" or maybe "I'll bet they are recovering from some injury" just to keep us humble 
As far as calling out, it depends. If I overtake someone who doesn't obviously know I am there, then I always call out. If we have been passing back and forth or riding fairly close together and are aware of each other, then not necessarily.
I was on a big organized ride last weekend and rode a little while with a lady who drove me crazy! She called out EVERYTHING... I appreciate that up to a point, but she was a just annoying after a while.
Grits
2010 Trek 5.2 Madone WSD, SI Diva Gel Flow
2002 Terry Classic, Terry Liberator