As handrawn explained earlier:

Xara uses 96 dpi and Illustrator assumes 72 dpi.

So an 3000 x 4000 pixel VECTOR drawing at 96 dpi in Xara is 31.25" x 41.67"

When you import that absolute size into Illustrator at 72 dpi (since you are dealing with size NOT pixels), the 31.25" changes to 2250 pixels and the 41.67" changes to 3000 pixels. you are always going to be dealing with a 96:72 (4:3) ratio.