Wasa-B is correct.
It isn't just that Silva is aggressive. It's that he's very, very good and knows how to make things work in NHB.
There are tons of guys, especially new naive fighters who think they are tough, who come out blazing figuring they will take their opponent out of sheer aggressiveness and ferocity. In the main, they tend to loose and often loose quickly. (See that big English guy against Fedor's brother in the recent Pride show).
Ferocity and spazzing out trying to clock a guy isn't enough in MMA, and if that was Silva's crutch he would have been exposed long ago. But Silva is very smart, very experienced, very well rounded and...as far as MMA goes very technically effective. He wouldn't be were he is if that weren't the case.
Remember that Jackson out techniqued Chuck Lidell, both in striking and on the ground in their match.
He out wrestled and out-struck Randleman (who KO'd Cro-cop). He beat Arona unconscious.
If you think Silva could beat someone like Jackson just by "spazzing out" and being aggressive, you haven't been watching this game very closely.