[Courtesy of Oliver Wilson, ocwilson "at" sunline.net, January 2000]
The 45 degree orientation is good for several reasons besides the strength of the glass fibers. It drapes better. It frays at the edges less. It resists the considerable torque loads imposed by ground loops better.
The strength of the glass cloth in compression is very little because the glass fibers are prekinked by the weaving process. Also, the thin lay up has a tendency to buckle under compression so that the material is only a little stronger than the epoxy for compression loads.
The best way to strengthen the fuselage is to use small radius crossections with thicker layups to resist buckling. Such a fuselage will bend under load instead of buckling and survive like the willow rather than break like the oak.
Using crossed layers of unidirectional material is also effective. The fuselage only has to be stiff enough to resist bending much under flight loads.