Walkers behaviors vary depending on a lot of bio-physical differences, just as living people all have differences and nuances in their behavior.
As the Yoga Instructor said in 'Couples Retreat', "There is such a thing as muscle memory, you know. And I can tell...your muscles remember."
Walkers smell decreases over time as putrefication completes it's cycle. They are also moving around, whereas the poor dead doggie basically decomposed on the floor and his liquids pooled and soaked into surrounding materials. Given that our crazed loner probably wasn't all that clean and still living he probably contributed more to the stink in the room, but our heroes didn't know that because they didn't know he was there when the lines were spoken.
We also adapt to odors after long term exposures. Our heroes are also fairly deadened to the basic scent, only a real lack of or an unusually strong odor even gets noticed now.
Michonne believes the Gov sent men to kill her, but can't conclusively prove it to our smitten Andrea in a way that would convince her. She was an attorney, yes? She doesn't take the world's evil for granted like Michonne does. A good Yin/Yang in many situations, but not this one. I also suspect that why she chooses partners who counter her views in every possible way.
I don't believe Andrea was an attorney. i think she just worked in an attorney's office. I believe Michonne was actually an attorney.