The Magen Avraham (44, 5) refers to the custom of fasting if a sefer torah or tefillin fall onto the ground. He does indeed use the words 'al haaretz'. (Seemingly the only difference between sefer torah or tefillin in this law is that one fasts for a sefer torah falling even if it was in its wrapping/container.) The Mishna Berura cites the Magen Avraham (40, 3.)
Piskei Teshuvot (vol 1 p.359) refers to Shut Afarkasta De'aniya that who says that this only applies if the tefillin fell onto the actual ground, however, if they fell onto a vessel that was on the ground one would not have to fast.
The Kaf Hachayim (40, 7) based upon the Ben Ish Chai does not rule that they have to fall onto the ground. If they fall more than three tefachim it is a denigration of the tefillin and one should fast/give charity. It is not important what they fell onto but rather that they fell from his hand.
According to the first opinion it is clear that something like a bimah is not considered part of the floor. At the very least it would be a vessel upon the floor.
Generally, there is a law of lavud, i.e. anything within 3 tefachim of the ground is considered part of the ground. For example, the Shulchan Aruch discusses this regarding praying on a raised area above 3 tefachim (90, 1). However, if the raised area is 4 x 4 amos wide it has a status as a separate floor (90, 2). The cases you mentioned of cars, trains and planes the floor would usually have the dimensions to be considered a floor in these regards.