Yeah, I also don't like this also, but it's set value in libvirt:

# vim src/qemu/qemu_driver.c +1214
static int qemuConnectGetMaxVcpus(virConnectPtr conn ATTRIBUTE_UNUSED, const char *type) {
    if (virConnectGetMaxVcpusEnsureACL(conn) < 0)
        return -1;

    if (!type)
        return 16;

    if (STRCASEEQ(type, "qemu"))
        return 16;

    if (STRCASEEQ(type, "kvm"))
        return kvmGetMaxVCPUs();

    if (STRCASEEQ(type, "kqemu"))
        return 1;

    virReportError(VIR_ERR_INVALID_ARG,
                   _("unknown type '%s'"), type);
    return -1;
}