Thank you, Annica5 and to everyone - thank you so much for clarifying this for me! I thought it was crazy that two epic dragons in one habitat couldn't make 10 gold/day. Now I know that they can (like I thought they should) and feel much better about my investment in purchasing a second habitat for when I can afford a third dragon.
I would definitely recommend saving gold for gold-producing dragons. They are awesome. Too bad I'm about to spend all my savings on this new habitat...