I have a friend ( somewhat PIMO) who does some freelance software work for the Society in the UK & Germany and he says the hotel commission the Society gets from conventions is incredibly lucrative. He told me to think in terms of a minimum of 1 million hotel rooms - 3 nights - $100 per room 15%-20% commission - that's close on $60 million alone annually tax free- and every year the Society grows this as they further develop relationships with the big hotel chains like IHG & Hilton and the likes of Expedia.
Add to this all the additional international convention income - my sister went to Canada a couple of years ago and I was astonished how much she paid for flights and excursions. ( Check out this brochure from 2009 - prices have more than doubled since then. ) http://www.wegieltours-wcs.com/parjw/parisbrochurewegieltours.pdf The Society , with its big building programs continuing and with a lot of legal expenses and child abuse payouts simply can't afford to give all this up.