ahhhh....a great discussion on gear masturbation.
go hold the cameras, take some pics in the store. Adjust the white balance, ISO and pic quality. While you're at it, with the camera in full manual mode, adjust the aperature and shutter settings.
Which camera feels the most natural? Buy it. I see you want just the basics, and there is nothing wrong with that. But I bet that as you take more pictures, you'll become interested in shooting other subjects.
As far as one camera "owning" another, WTF ever. That is a very uninformed statement. As far as the D60 over the D40x, the 60 doesn't really bring enough to the table. I've been shooting for a while, and I even make a little money at it, but I do it becuase I enjoy it. The camera you choose doesn't make a shit worth of difference, the pictures you take do. And I can take the same picture with the Sony that I can with the Nikon. One may have a bell or whistle that makes it a little easier, but really, at that price point, just pick the one that is more comfortable to hold and use.
If you have any inkling that you may stay with photography, compare Nikon to Canon. You have better upgrade options as time goes on.
1999 e46 328i Ti Silver / Black[retired]
2007 e90 335xi Jet Black / Black[retired]
2011 e70 X5 35d Vermillion Red / Cinnamon
2011 e92 M3 LeMans / Fox Red extended