According to this article, the application vault is now included with 10.4. Both me an my clients are unable to see the application vault in the control panels (assuming it's a tab like it always was). I can see an icon in tools & utilities page for it though.
The following features are available on the Plesk license by default. Before the version 10.4 it could be used only with PowerPack. Since 10.4 PowerPack is not required for it.
Spamassassin
Application Pack
The following features are available on the Plesk license by default. Before the version 10.4 it could be used only with PowerPack. Since 10.4 PowerPack is not required for it.
Spamassassin
Application Pack