A key difference between maven and Ivy is that maven nature is intended for a single module output. Ivy is designed instead for multiple output artifacts from the same component.

Maven is probably more suitable for the intermediate, most developer centric processes (structured activities) while and Ant is useful in the last steps of delivery, where you may need to add specific tasks, consider configuration and adjustments depending on user needs, client requirements, device configuration, different channels, etc.

Obviously there are newer alternatives, but Ant and Ivy, due to the shared Xml format with Xslt, Xproc and content formats like dita, docbook, etc. seems like the natural match for the job.