When doing side-by-side testing, it is difficult to tell which is WebKit and which is Safari. If the application names in the menu were different, testing would be easier. The Cmd-Tab icon/name are different, but that requires an active step, rather than just visually checking the menu bar.
While it would be nice if we had something like this, I'm not sure we really want to embark down that path. There is already a lot of confusion over exactly what you get when you download a nightly (many people think you get a completely new version of the Safari browser as well as the WebKit frameworks) and changing the name would blur the line of distinction between Safari and WebKit line even more. From a technical perspective, we already do a fair bit of hackery to get the nightlies working and doing this would involve more hackery that could cause Bad Things(tm). Mark will know for sure whether or not we really want to do this.
I doubt this can be done without resorting to something really hacky. The name on the application menu is hard-coded in the NIB file, so to change it we would need to poke around inside Safari 's data structures at runtime. I'm not sure that is something we should be doing.
I spent a while digging around to see how hard it would be to do this, and the answer appears to be "very". There is no supported way of changing the application menu title in your own application at runtime, and doing it in another would be even more complicated again.