Whether you call it a coin or a share or something else depends on the utility. If all you can do with it is send to another user, it tends to be called a coin. In Bitshares it is referred to as a share.

Accounts on most of the primitive blockchains are indeed long sequences of characters, while on Steem and Bitshares accounts are names. Coins themselves are usually just a balance on the ledger, and have no identity. Safecoins on the Maidsafe network however will have an identity - they are each unique, and can still be splitted.

What gives the coins or shares value is the utility or the community. Check out Daniel Larimers early post on Steem about why STEEM has value. Keep in mind that STEEM is just a balance on the Steem ledger (blockchain). Here's the article: https://steemd.com/steem/@dantheman/why-people-will-buy-steem