The definition of "owned" in the ARIA spec includes any descendant (or any descendant of a node that's aria-owned).

That means that according to the spec, it's okay to have a list with listitems that are descendants but not direct children, or a grid with rows that are descendants but not direct children, e.g.:

<div role="list">
  <div>
    <div role="listitem">One</div>
  </div>
  <div>
    <div role="listitem">Two</div>
  </div>
</div>

<div role="grid">
  <div>
    <div role="row">
      <div>
        <div role="gridcell">1, 1</div>
      </div>
      <div>
        <div role="gridcell">2, 1</div>
      </div>
    </div>
  </div>
</div>

In practice, this doesn't seem to work with *any* browser or screen reader, unless you use aria-owns or role=presentation.

It occasionally works in some circumstances when the browser skips over extra unneeded container elements - but it definitely doesn't work in general.

Either the spec needs to better match how browsers and assistive technology have implemented their support for owned relationships, or browsers need to start doing a lot of extra work to search all descendants for required owned elements.