bc and dc are arbitrary precision. By using -l you are specifying that it should keep track of 20 decimal digits (plus you are importing some extra stuff).

You can try higher precision by setting the scale.

    $ echo "scale = 100; (2/3)*3 - 2" | bc 
    -.000000000000000000000000000000000000000000000000000000000000000000\
    0000000000000000000000000000000002