Those are pretty standard parameters for shows.
When they say "ease", what they mean is the front face of the sleeve can't lay flat against the quilt. This is because if you DO sew a sleeve with no ease, when the quilt is hung there will be a bulge on the front of the quilt. The dowel or board takes some space, and if you don't allow space in the sleeve, it will take it from the quilt, which then won't hang as nicely.
If you look at the very last picture in the link that feline fanatic posted, you will see very clearly how the front face of the sleeve doesn't lay flat against the quilt.
The 4" seems excessive until you see how a lot of shows use large dowels, and personally I'd rather have lots of space when a volunteer is shoving a wooden rod into the sleeve.
Nothing against volunteers, and I appreciate all the hard work they do to make the shows happen. It's just the nature of hard wood vs. soft fabric.