osgeo can be used after installing GDAL (https://pypi.python.org/pypi/GDAL/).
The towgs84 parameter is not always mentioned in a specific Coordinate System definition. If the towgs84 clause is contained in its definition, then this should be its "preferred" transformation. The clause towgs84 may not be included in the situations described here.
What is towgs84, actually? As written here, datum shifts can be approximated by 3 parameter spatial translations (in geocentric space), or 7 parameter shifts (translation + rotation + scaling). Those datum shifts can be described using the towgs84 parameter.
Without +towgs84 correction, the tranformation uses the official epsg:28992 definition. That gives a slightly different, erroneous result, which is in the order of ~1 cm for the point selected.
Alternatively to EPSG:28992, we could use another Amersfoort / RD New Coordinate System definition, which contains the proper towgs84 parameter, the SR-ORG:6781. Its Proj4 format is described here. As EPSG:28992, this is an oblique stereographic projection (see definition here).
See the difference with EPSG:28992 (without towgs84):