There's a big discussion between the various agencies that make recommendations on floor structures to spec things for tile installations. The current recommendations are to set a limit on deflection, but the newer thoughts are to design for the actual load rather than some arbitrary spec, like the 40/10 mentioned. One thing to keep in mind on that is that the entire subfloor and finished material makes up that 40 pound value. Throw on some cement board, and extra layer of ply and maybe some leveling compound and a stone tile, and you may have used up your entire dead load without any furniture or appliances. One other thing that is part of this whole discussion is long term creep of the structure. While a tiled floor might survive with the current spec for awhile, but, especially with dimmensional lumber, a constant heavy load can cause it to gradually continue to bend and the floor to fail. The Tile Council of America personnel were asked to investigate just this problem and this started the discussion of 'is the current means of specifying floor structure adequate to ensure long-term survival'.
This may be totally off topic for what your objective of the original question was, but I thought it was interesting, and might be very pertinent.