So it turns out that without the replaceInExtensions option, replacements won't work. I had to put that in to get replacements to work. A suggestion for updated documentation would be
gulp.task("revreplace", ["revision"], function(){
var manifest = gulp.src("./" + opt.distFolder + "/rev-manifest.json");
return gulp.src(opt.srcFolder + "/index.html")
.pipe(revReplace({manifest: manifest, replaceInExtensions: ['.html']}))
.pipe(gulp.dest(opt.distFolder));
});