Hi Tech,
Yes, my friend, the new malware technology (Web 2.0 interactivity) and developments make various detection methods necessary. To rely solely on signature bases is an archaic procedure, but it certainly has not lost its usefulness. I think that lacking heuristics also plays a roll in the placement of avast's scanner, but that is a decision the developers made, and they seemed to have contemplated that on good grounds.
Other methodology should be brought in as well to make the balance is not tipped over in advance of the malcreants. I already use a cocktail of programs to keep my box secure, alas there is no other way...
polonus