It's actually 87 lines of code, with a disclaimer comment, ample empty lines, a callback to play a wav when clicked, and an error message for when it's not run on NT. So, like 30-50 lines of actual Hello World necessary code. And that includes the starting up boilerplate.

Petzold's Hello World is far more than what I'd consider a Hello World in Win32, because in addition to what you noted, it also creates a "full" window with all the associated complexity of managing its drawing yourself. A more suitable Win32 Hello World is not that much more complex than the traditional C one:

    #include <windows.h>
    #include <winuser.h>

    int main() {
        MessageBox(0, "Hello World!", "Hello World!", MB_OK);
    }

From there, one can progress onto "dialog-based applications", where the bulk of the layout is declarative (in the resource file) and the C part is two functions, a callback for messages and a main() which just calls DialogBoxParam(). No WM_PAINT handling is necessary for those. A "full window" application is actually not necessary for many use cases. I've been working with Win32 for over a decade and a half and written at least a dozen little apps for various things, but the vast majority of them are not "full window" apps.

In other words, I'd say Petzold was at least partially responsible for giving the impression that Win32 is impossibly complex even to start with. Fortunately others have come up with better introductions like http://www.winprog.org/tutorial/ or even https://win32assembly.programminghorizon.com/tutorials.html since then, but it seems that the damage has already been done and a whole generation of programmers have gotten the "Win32 is hard" notion embedded into their minds.