Availability of sectioning commands in menu

In course of fixing the menu for sectioning commands (it does not work
correctly across files with different document classes and does not
get updated if new sectioning commands become available) I found an
oddity concerning the available commands.  In none of the supported
document classes it is possible to use \part via the menu.  In
style/book.el, for example, we can find

(setq LaTeX-largest-level (LaTeX-section-level "chapter"))

Does anybody understand the rationale here?

Personally I'd use "part" instead of "chapter" (and in the style files
for other such document classes as well).  The logic of having a
largest level is flawed anyway because \part can be used even in an
article class, but changing the respective definitions in the book-
and report-like classes should improve the situation at least a bit.

-- 
Ralf