No, look;

In Series 2 (there were a few seeds then), Mortis, the 2nd seed (who DIDNT finish second!), was beaten by Panic Attack in the last round of the semi-finals.

In series 5, Pussycat was beaten by Firestorm in the last round of the semis.

In series 6, Bigger Brother was beaten by Terrorhurtz in the last round of the semis.