here are two examples where javascript-added ads can be blocked in b2 but not in b3 nor b4:
the rules i use:
tradedoubler\.com/
layer-ads\.de/
Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Adblock-tests</title>
</head>
<body>
<script language="JavaScript" src="http://impde.tradedoubler.com/imp/js/11478095/1119837?123" charset="ISO-8859-1"></script>
<script src="http://layer-ads.de/la-7732.js" type="text/javascript"></script>
</body>
</html>