Why the `click' modifier for a mouse-wheel event?

["Drew Adams" <drew.adams@oracle.com>]

Subject line says it all.

In Emacs 22 (and 21, 20...), using the mouse wheel did not add any modifiers to
the event that was read.  In Emacs 23, `event-modifiers' for a
`mouse-wheel-down-event' or `mouse-wheel-up-event' returns `(click)'.

Why? Is this a bug or a feature or just an inescapable implementation
limitation?

This behavior doesn't seem right. Using the mouse wheel (without pressing it to
realize a click) is not the same as clicking a mouse button.

(I'm using Windows, so the `event-basic-type' for a wheel rotation is `wheel-up'
or `wheel-down'.)