And it's doubly hard because the audience is almost always something of a mix. I've given more than one presentation where the survey has included some variant of both "Way too basic" and "Went way over my head."
* Too much information is usually better than too little. You can organize the extra information into separate sections, which makes it easier for the advanced audience to skip over. * Prioritize one audience over the other.
In the case of presentations I'd probably stick to prioritizing one audience over another. Given a room of people, who is it most important to transfer knowledge to? Better to make half the room happy, than none of the room.
There's more of a commitment in a presentation. It helps to advertise things accurately. Although there's no shortage of people who come to an "Introduction to" talk and expect it to be deep in the weeds.
I once gave Unix and C training (two separate courses) to a group of experienced corporate IT developers (at a large Indian public sector company, Hindustan Aeronautics Limited). When I was explaining some of the finer points of pointers (pun not intended), like star star argv (pointers to pointers etc. - in the C course), one of them said: "now it is overhead transmission" :)
And the motivation was partly practical. Inverted pyramid lets an editor cut a story at a more or less arbitrary point in order to fit it in a hole of particular size on a page. This is/was particularly true of wire service copy.
We tried a lot of different approaches and you still end up with some audience members whose expectations are seriously out of tune with the content of sessions.
Of course, sometimes there's fault with the presenter too.