Alan W. Irwin wrote
So, an
app which uses the plplot wxwidgets driver cannot be distributed as an
executable image.

That conclusion is incorrect.  If you link your app correctly, and supply
all the required bits and pieces of PLplot, there should be no problems.

The whole point of shared libraries and plug-ins is to keep logically
distinct things separate rather than putting all code into one giant
library.  This approach actually minimizes the size of what you have to
distribute since you only have to include the bits and pieces of PLplot that
you need rather than everything.  However, the trick is figuring out the
exact bits and pieces that you need (see below).
You should regard the wxwidgets driver like any driver: most require support from
external software. The exceptions are the PostScript driver and several others, but
you can not usefully do anything with the output unless you have software and
hardware to display PostScript files on the screen or print them on paper.

In a very similar way any driver that displays the plot in a window on screen relies
on system software that is already present, be that X Window or MicroSoft's Windows
or whatever. You do not deliver that as part of your application. And you do not need
to use wxwidgets, as there are plently of other device drivers available.