Thanks choroba for setting me straight. If there's one thing that I keep forgetting to learn it's not to post regex questions or answers in haste. ;)

You are correct. This:

local $_ = 'foo';                         
                                          
m/\Gfoo/gc && say 'Matched foo';          
m/\G.+/gc  && say 'Matched dot star';     
m/\G\z/gc  && say 'Matched end of string';
[download]

...produces this:

Matched foo
Matched end of string
[download]

And this:

local $_ = 'foo';                         
                                          
m/\Gfoo/gc && say 'Matched foo';          
m/\G.*/gc  && say 'Matched dot star';     
m/\G\z/gc  && say 'Matched end of string';
[download]

...produces this:

Matched foo
Matched dot star
[download]

...indicating that end of string was consumed by dot star, though it's still a little odd because this also matches:

local $_ = 'foo';                      
                                       
m/\Gfoo/gc && say 'Matched foo';       
m/\G.*\z/gc  && say 'Matched dot star and end of string';
[download]

...produces this:

Matched foo
Matched dot star and end of string
[download]

So while it may be eluded to in the documentation it's not entirely unsurprising. :)