That is not what is being said.
The "main" SpywareTerminator download includes the crawler toolbar with web security guard (WSG) - sort of like "site advisor", but a bit better, AFAIK.
(Required to be installed for "Internet Protection", but nothing to do with "internet explorer protection" located in the "Real Time Protection" area.)
It also includes the (optional) Clam AV, which uses the WinClam definitions and cleaning engine, and by a software trick known as "magic" avails itself of the antispyware's resident protection shield. So it's a way of turning the normal demand-only WinClam into a resident.
I have run ST, with Clam, and Avast Home together in the past, for a few weeks, with no problems; I believe they do not conflict, because of the different types of resident protection.
That is not to say they won't conflict: it is certainly possible, I've not had it, and not heard of it.
I've since uninstalled Clam simply because I don't consider it necessary in addition to ST and Avast.
I've never had the WSG installed, not anything against the crawler toolbar at all, I just don't use toolbars, full stop. Apart from what's already in Firefox.
Makes for a much better viewable screen, and less cluttered processes.
On the SpywareTerminator download page, the standalone version is the second download, 4.53Mb. This is the version I use, and have been problem (and malware) free.