Tubes and I beams act exactly the same.  The web, or walls are just there to connect the top and bottom plates, by the moment of inertia formula below, you will find that nearly all of the strength comes from the top and bottom plates, due to their mass being most distant from the center point due to the distance squared term in the formula.  I beam just connects the two plates in a more efficient manner.  If the tubing has walls half as thick as the single web in the I beam, the capacity would be identical in the vertical direction, not in the horizontal though.