I don't get this either.
The phenomenon may be somewhat poorely explained in the article .
Sure Jupiter is capable to clear a gap in a molecular cloud or asteroid belt around him .
Sometime ago I made a simulation of Jupiter , originally surrounded by lots of space debris .
The effect of Jupiter may be seen here :
http://www.orbitsimulator.com/cgi-bi...num=1189853529
( see reply nr #7 in this topic )