Why would the trustee be excluded from being a beneficiary?
Some people are of the view that allowing the trustee to be a beneficiary may invalidate the trust - or at least that any distributions by the trustee to itself may be difficult to justify in light of their fiduciary duties.
Of course, we are reliant on the courts in establishing what trusts can and can't do. In a recent case in the Victorian Supreme Court (Ailseen Pty Ltd v One Hawker Holdings Pty Ltd & Anor  VSC 135), not only was the trustee also a beneficiary of the trust, but the settlor didn't provide the settled sum and his signature was forged and the trust was still valid!
That said, we do not advise this course of action.