This question is a good one for the official Q&A.
3/4 inch thick (nominal) plywood really is very close to 3/4 inch thick.
3/4 inch thick (nominal) solid, robust wood may be thinner, as you pointed out.
My understanding is that the actual thickness of the plywood or solid, robust wood must be 3/4 inch, or very close; e.g.,
23/32".
As a side note, good quality 3/4 inch plywood is more impact resistant than many kinds of solid wood.
__________________
Richard Wallace
Mentor since 2011 for FRC 3620 Average Joes (St. Joseph, Michigan)
Mentor 2002-10 for FRC 931 Perpetual Chaos (St. Louis, Missouri)
since 2003
I believe in intuition and inspiration. Imagination is more important than knowledge. For knowledge is limited, whereas imagination embraces the entire world, stimulating progress, giving birth to evolution. It is, strictly speaking, a real factor in scientific research.
(Cosmic Religion : With Other Opinions and Aphorisms (1931) by Albert Einstein, p. 97)