Hi mouniernetwork,
I do not know why avast did not develop something similar, but they have not. The update rate of DrWeb is very accurate. With this particular plug-in you scan all your hyperlink on their servers in St.Petersburg, nothing enters your machine, only their scanning report. It is rather unique. And you occasionally scanning with an online non-resident scanner like Bitdefender or downloading the DrWebCureIt or Stinger.exe for a second opinion, or having the extra protection of a non-resident open source scanner like ClamWin together with the ClamWin Glue add-on for Firefox, all this does not hurt Avast. You have it there for additional protection or a second opinion. You sure are not only visiting one doctor in your life, do you? Or feel a moral obligation to do so, but you have one private GP. Well it lies in a similar line, as far as I can see. Every malware vector stopped is one that does not land on your machine. Simple as that. DrWeb plug-in is only a browser add-on, not part of a resident AV-solution like Avast's WebShield. These are two complete different things, my friend.
Have a great day, and enjoy it,
polonus