That is a problem with HIPS, in general. A novice user can be "tricked" into ignoring HIPS pop-ups. A good AV will block the threat and quarantine it automatically. Even if it prompts the user with a warning: "This file is infected", I'm sure that most users will choose not to run it. So AV-s are still needed (even for prevention). I don't expect an AV to block all malware, but I certainly expect it to block most of it.