Not true. Internet Explorer used to work with both NSAPI and ActiveX plugins, until they pulled support for the former.
"""Netscape-style plug-ins are supported in Internet Explorer 5.5 Service Pack 1 (SP1) and earlier, but are not supported in Internet Explorer 5.5 Service Pack 2 (SP2) and Internet Explorer 6."""
-- http://support.microsoft.com/kb/306790