I have my last BMW, and the battery situation is one of the reasons. My Lexus is my DD, and there are many days I drive it less than 5 miles. Battery discharge has never been an issue, even after it sat for almost a month, although I now (illogically) install the Deltran if it's going to sit more than a week. I guess it's force of habit from the BMW.
BTW, some time ago I brought up the BMW battery issue to my Lexus SA, and he looked at me like I was nuts - said he never experienced anything similar with a Lexus, and certainly doesn't have a 'checklist' of dos and don'ts like Kat received.