One of the other things that makes SQLite different is the ability to define scalar and aggregate functions, as well as collations, on the fly.  Once you have installed the gamma function, for example, you can write GAMMA in SELECT or WHERE clauses.  The Python APSW library, for example, lets you write these functions in Python, and there is no problem with writing them in Scheme, at least in principle.  It's true you can do similar things in Postgres and My, but you have to be able to install the appropriate language support on the server, which is nowhere near as flexible.