Ok I got it.....I deleted horizontal edges but DID NOT use the delete edge/vertex....so there are undeleted verts that are causing mine to create the seam. Select your object, take note of the verts and either merge or delete...see if that changes it. Then I started adding edge loops...they slowly went away...so it must be the UV editor trying to interpolate from the bottom to the top....you must have no edge loops in between?

cheers bullet

EDIT: It is the lack of edge loops by the look of it mate...I just had a glass with no edge loops on the body...had the seam..then selected all those faces and added divisions...it disappeared.