Clare it is a pleasure to answer your questions because I think you ask with a true desire to learn.
The seam you ask about was probably created by the mold to create the item. The manufacturer should have cleaned up the seam with filing and chasing. You are right in assuming that most of the items with visible seams in castings are poorer quality than those items where the seam is nearly invisible.
The items you have described were both made by the process of casting. The are probably cast in a low temperature metal similar to pewter. They are usually reproductions of items that were originally handmade from sheets and bars of silver and then decorated by a process known as repousse and chasing. Some items are decorated with finely cast fruit or scrolls. It takes a keen eye and visits to museums and high end antique stores to learn to distinguish the good from the bad. There is nothing quite like being able to handle well made items and to be able to use them for the purpose they were made.