i know its an incentive to get people to go fight for bosses, but to the best of my knowledge that happens seldom, or at very easy to get to bosses (ken). the only thing announcements really do that i can tell is tell specific people to log into specific characters and go solo them in 30 seconds then swap back.
sure the announcement is nice and it probably does get bosses to be killed slightly more frequently, but i don't know the goal if the only pvp it creates is at ken or maybe dg or chaos. what it does create is laziness in looking and just waiting for announcements.
and lets face it, 2 of the most important of 10 important bosses don't announce anyway, varlok and yahee. the other 8 i firmly believe shouldn't announce either (9 for safe measure but 9th doesn't have a drop). and all of those are killed pretty much on cooldown. no ones ever complained about varlok not announcing.
and with added value in all bosses dropping runes, i feel like time commitment to actually go check is even more important. and only select bosses over lvl 75 dropping legendary runes, you shouldnt need to be told to go. value is already there. and yes im aware of hardmode dropping runes too.