Why is hydrochloric acid often sold as 33% concentration?
The user ssavec prompted me to research further on my own and post an answer.

It seems the limits are practical ones.


For hydrochloric acid — $\ce{HCl}$ a practical limit is 38% with absolute
limit around $40~\%$ and commercial concentrations ranging from 30 to 35%
for convenience in transportation infrastructure.
For nitric acid — $\ce{HNO3}$ the $68~\%$ limit is the maximum that can be
reached by direct distillation, higher concentration up to $98~\%$
(fuming nitric acid) needs alternative dehydration or synthesis techniques.
For sulfuric acid — $\ce{H2SO4}$, which can be distilled to $98.3~\%$ (and can be used
to concentrate nitric acid) it is sold at concentrations that are
directly suited for the intended use ranging from $20~\%$ to $80~\%$. With concentrations around $30~\%$ common for lead-acid battery electrolyte preparation.


So it seems the limits are all practical but for different reasons, one was close to the absolute limit for efficient transport.  The second was at the direct distillation limits and the last one was to suit the most popular consumer applications.

The spread in the numbers had caused me to wonder on their relation but it seems there was no direct relation to the concentrations we see for consumer sale.