Because modern coins are struck in a collar to provide uniform flow of metal, uniform thickness, and uniform diameter. As such, you need to strike within a collar to meet these specs. The reason some are reeded or have words in them originally was to prevent thieves from shaving PM off a coin and making a coin lightweight but pass it off for full value, and profiting from the PM shavings. With base metal coins this is not a concern, but we keep them for historical sake.
Because of the incused design I would say so. Even though I find these type of coins to not look as nice as normal ones, from a practical standpoint they are much better when trying to preserve the design through out wear.
The GDR had an interesting "policy" regarding rims or raised edges: Most coins, including commems, had them - but the silver pieces that were made primarily for collectors in the Federal Republic (and other non-socialist countries) usually had no rim. That, together with the higher relief, makes them more attractive among potential buyers. But with coins that are supposed to circulate for many years, even decades, it makes sense to have a rim that to some extent protects the coin from wear. Attached are two GDR pieces which both commemorate some jubilee (Wagner, Luther). But the 10M silver piece was made solely for collectors, while the 5M Cu-Ni coin had a higher mintage. The latter was not issued as a circulating coin but may have occurred in circulation ... A circle of pearls, however, is (for modern coins) purely decorative indeed. Christian
