Thanks for the suggestion; it actually led to an interesting discovery:
With the keybinding set to (kbd "C-x<escape>"), running "C-x<escape> C-h"
(in a terminal session, since in a GUI one it quits Emacs) shows the following:
Global Bindings Starting With C-x ESC:
key binding
--- -------
C-x ESC ESC repeat-complex-command
This got me thinking about the fact that the help system is calling it "ESC",
not "<escape>", and wondering about whether that is significant.
I then tried changing the binding to (kbd "C-x ESC"), which actually works in
both graphical and terminal sessions!
In conclusion, it looks as though there is a difference between "ESC" and
"<escape>", at least as far as the "kbd" macro is concerned. I don't know
enough about the topic to be sure, but I would speculate that "<escape>" is
some sort of special meta-character being sent by the X window system, while
"ESC" is the lower-level key value.
Very interesting stuff; and it now lets me use the more readable form, too!
I'm still quite curious about the discrepancy, but at least the original
problem is solved. Thank you!