It's interesting that the article doesn't address this, but the reason I think that relying only on cellphones without a landline is risky has to do with emergency situations, and for some reason I thought the CDC would tie into that, but maybe I've just been watching too much of the walking dead.

In the case of a cellphone-only household, it's really easy to think of a time when all of the cellphone holders are not present, so that there's no real contact into or out of the house, potentially with people present. In the case of a 911 situation like someone choking or having a heart attack (or a fire) that could come down to going up and down the street knocking on a neighbor's door, or jumping in a sedan to race to the hospital.

I also wonder how accurate geo-location would be for 911 calls, where it's very easy (I would hope) for 911 operators to know the exact street address of someone making an emergency call, even if they ask for the address as well.