I was thinking the same thing, as a current volunteer firefighter and techie I've thought about firefighting robots for years.
There are some huge obstacles aside from the most obvious which is heat.
- Terrain, as you said is a big one. I have been in a house with 2 feet of trash and laundry through the whole house. We could not see the floor while we were there. For humans it was a challenge, but for a robot it could make it impossible.
- Strength - As you know shagging hose takes strength, and that comes at a price for robots (weight and power usage).
- Victim Removal - While it's not an everyday occurrence its definitely a factor. What if someone is in the house and needs to be removed? Can a robot do this without further injuring the person? Does it have the dexterity to maneuver out of there towing someone?
- Deployment time has always been a big one. Can a robot do a scene size up? Not really. Can it do a 360 across any type of terrain that the house might be on?
I have no doubts that someday robots will be fighting fire, but we're such a long ways away from it still.