The ones folks are buying? Not really. :D Publishers still do a good job signing on authors. Audio books, I think, are very different. Audible was far more active in building up a market and voice talent than the competition for a long time.

That said, I am not aware of any actual anti-competitive practices that they do there. The examples that some high profile folks have used feel very weak. Prices are lower for customers than they have ever been, and profits for the talent are almost certainly up due to increased sales volume. Their percentage profit per sale is down, but the history could also be that keeping that percentage high would not have grown the market? Such that, they could not have gotten the larger pie without the smaller slice. But, now that the pie is big, they want the bigger slice.