What is wrong with this picture?

This picture is my inspiration for a set of shelves.  After some head scratching, however, I have discovered there is something wrong with the design presented.  The back of the unit uses pipes 24 inches long, and the shelves themselves are 24 inches long.  Unfortunately, the designer does not take into account the addition of the T joints.  When one connects T joints, one has to account for their width in the separation of the supports as well as the loss of thread length on the pipe itself.  For example, if ¾-inch diameter pipe is used, this will add approximately 3 inches to the measurement.  The 24-inch long pipe with a T on each end is now 27 inches long.  This creates a gap between the supports of 25 inches, so the supports are too far apart to actually hold a 24-inch shelf, as pictured in the diagram.  The simple answer, then, is to use 18-inch long pipe for the back of the unit instead of 24-inch.

Further, this diagram does not make clear what diameter of pipe is to be used*.  Black pipe, which is part of the diagram's name, comes in many diameters.  I suppose I will have to see what my hardware store carries in the parts I need to decide which diameter to use.  My fear is still that the unit, as designed, will bow downward from the top due to all the joints.  I am going to have to buy proper pipe tightening tools to make sure the joints are as secure as possible; I am also going to continue the cost-benefit analysis before buying anything.

The pictures on the page appear smaller than they are.  To see them larger, simply double click on the picture.  Also, I always welcome your constructive criticism.  Click on the Comment link below next to the icon of a pencil; it may say “No” or have a number in front of it.

*I stand partially corrected on the diameter point.  While the diagram itself does not indicate pipe diameter, the information on the designer's upload page indicates this is to be 1-inch diameter pipe.

References:
J., Jamar. "Black Pipe shelve." SketchUp 3D Warehouse. Trimble Navigation Limited, 26 Mar. 2014. Web. 9 June 2014.