What are the primary architectural differences between the backup formats of some of the more common RDBMS' and what advantage do they serve?
The native backup of sql server, commonly have extension of .bak is something which is proprietary of microsoft.

Different RDBMS providers have different formats and it also depends on whether they are open source (PostgreSQL and MySQL) or are patented (MS SQL Server, ORACLE or SybaseASE).

For MS SQL Server :

A backup is a page-by-page copy of the database, as it existed the moment you took the backup, a restored copy of that database will be in exactly the same state as it was the moment you took the backup.

A backup contains more than just the data. It contains the entire structure of the database including all the data structures and data along with procedures, views, functions and any other code. It also contains the settings and definitions of the database along with the users of the database. Exception is contained databases have a concept called USER WITH PASSWORD.

If you want to use something that you mentioned, have a look at SqlDump - Microsoft SQL Server database backup program


  SqlDump is a program to backup a Microsoft SQL Server database as a text file. SqlDump generates SQL statements for tables, indexes, user-defined types, views, procedures, etc and also the table data. This data can be used for a variety of purposes, such as database backups, moving databases to another server, or setting up a test database based on the contents of an existing database


Note: I have not tried the SQLDump, as I would personally prefer SSIS or T-SQL along with BCP and BULK INSERT - to move data out and in of sql server.