Why haven't Earth and Venus got any tiny moons? Or have they?
The strength of the Earth's gravitational field compared to the Moon and the Sun is not enough to capture and hold satellites - there are too many disruptive forces that would rip them away over time.

However there are some objects at the Lagrangian points - the points where the gravitational fields of the Earth and other objects are equal and so it is possible to have a (likely-meta) stable orbit. 

This gives some details about what might be found at the various Lagrangian points: http://en.wikipedia.org/wiki/List_of_objects_at_Lagrangian_points