There are clearly barleywines which wouldn't be considered IIPAs, and IIPAs that wouldn't be considered barleywines. While there is often overlap, because both are high in alcohol and hoppy, some of the more dry IIPAs these days could NEVER be called a barleywine. And some of the maltier barleywines wouldn't fit in the IIPA category.
Yes, a lot of American craft brewers have darker, maltier IIPAs. You could just as easily slap a "Barleywine" label on them and nobody would really bat that much of an eye. But could you do this with Pliny? Ruination? Hop Stoopid? I don't think so.