I think the modern icons are striving for a more abstract and minimalistic look. This seems to be the case for all 3 mobile OS covered. This is mostly about fashion, I guess, but an abstract icon does look less out of place in more situation. I can well imagine being slightly miffed about having to put a megaphone in my app to fit platform conventions, although I would gladly take it over that god-awful present icon WPOS7 apparently had.