Thanks for your replies. I understand the allergy comment but from what I know there are certain areas of the hotel that are for pets so if there are allergies they can stay in another wing.
$100 over an extended stay isn't the end of the world but for 1 night it's significant and almost doubles the cost.
One thing I did notice is the hotel web sites don't clearly disclose any fees associated. The Residence Inn I'm considering (and another Marriott nearby) advertises being pet friendly right on their home page with absolutely no reference to an added cost. I didn't notice anything in the booking process either. I looked further and it was buried in a hotel details page. One could just book the room and be in for a big surprise when the get to the hotel. There would be a good case to challenge a fee that wasn't disclosed.