"only two but the eggs will be split three ways and the other third will go to the egg bank"
That is amazing. I can completely understand your annoyance. I just went through the whole orientation program at at SG just before you did and that scenario was never presented to me. Rather it was presented more as you were thinking - that if no match was made whatever eggs are retrieved are split by two recipients. Considering the recipient fees are paying for the meds and effort of the donor cycle, SG basically gets free eggs to resell.
On the other hand they could make you wait indefinitely for another recipient to sign on to the cycle so in another sense they are doing you a favor. You still pay less for your cycle then someone doing a 1:2 split (like me) and I am sure that the recipients in the 1 and 2 position take priority over their egg bank.
Have you had a chance to look back over the contract? It would be curious if they did not spell out this scenario in the documents.