On Monday 14 of December 2009 18:50:55 Bart Schaefer wrote:
> 
> Aside:  I can't find the "var=value command ..." syntax anywhere in
> the zsh manual.  I was sure there was some mention of it,

As far as I can tell:

6.1 Simple Commands & Pipelines
===============================

A _simple command_ is a sequence of optional parameter assignments
followed by blank-separated words, with optional redirections
interspersed.  The first word is the command to be executed, and the
remaining words, if any, are arguments to the command.  If a command
name is given, the parameter assignments modify the environment of the
command when it is executed.

May be, what is missing - explicit statement that if no command name is 
given, parameter assignments modify current shell.