If two objects are touching, ST_INTERSECTS() reports false and ST_INTERSECTION() reports an empty value.

By contrast, the postgis documentation says:

Overlaps, Touches, Within all imply spatial intersection. If any of the aforementioned returns true, then the geometries also spatially intersect.

In postgis, ST_INTERSECTS() will return TRUE and ST_INTERSECTION() will return a POINT

examples:

SELECT ST_CONTAINS( GeometryFromText(' POLYGON(( 1 1 , 1 9 , 9 1 , 9 9 , 1 1 )) ') , PointFromText(' POINT(1 1)' ) ) ;

SELECT ST_INTERSECTS( GeometryFromText(' LINESTRING( 3 3 , 3 0 ) ') , PointFromText(' POINT(3 0)' ) ) ;