As I understand, that's less powerful, because you can do:

    t"INSERT INTO mytable VALUES ({s}, {s[::-1]})"

but you can't do:

    mydb eval {INSERT INTO mytable VALUES ($s, [string reverse $s])}

Instead, you have to write:

    set t [string reverse $s]
    mydb eval {INSERT INTO mytable VALUES ($s, $t)}

There's no reason you couldn't have such power in Tcl, though: it's just that the authors of SQLite didn't.