Planets observation of a missing definition of low and high value is worth noting. Noone knows where the line is drawn.
Lets put it this way - if I went off and did 300, 40,000 link xrumer blasts against my competitor with the right anchors (IE what the competitor would WANT to rank for) then I guarantee - my competitor would fall. Just to be certain though - I could easily join 30 or so paid link schemes and plaster his site all over that aswell.
If he didnt fall - then I surmise that google must have an "this is an obvious attack" detection system. One attribute of this could be an answer to the question as follows :-
"why would a high ranking site blast itself"?
One can easily see that 90% of malicious blast attacks would be done against top 10 sites - 80% of those are probably top 3. It follows therefore that blasts on low ranking sites would typically be spam blasts where the blaster hopes to gain rank - and blasts on high ranking sites would typically be attacks against a competitor.
It is easy to program a computer to calculate probabilities and act accordingly.