These services generally provide a service that is not part of standalone bitcoin, whether that is a payment API which generates addresses and verifies transact

These services generally provide a service that is not part of standalone bitcoin, whether that is a payment API which generates addresses and verifies transactions for customers, an exchange to trade and value bitcoin based on fiat currency, or a user-friendly wallet that allows access from anywhere with internet access and bypasses the need for a user to download and update their own copy of the blockchain. (The blockchain is pretty large. It currently sits around 13GB and is always growing.) There are also end-user applications like Armory, which are meant to manage and secure a wallet on an end-user's machine, but its inevitable that people will use online services for foreseeable future.