I suppose that statement and the linked article could lend itself to thinking that one should see a difference in cmyk vector objects.

Try this. Use an rgb image. Especially one with color way outside the cmyk gamut. Then switch profiles. That should show up differences.

However, I do not know how Xara is handling...assign or convert when importing an rgb image. If they are even dealing with the issue--but one should have a choice. Using assign, one should not see a difference, or much of a difference between cmyk models except where ink limits affect the characterization. Using convert, one should see an obvious difference (depending on the image) between the image editor and XDP+.