Something many of you have not thought about in this discussion.
Houses/Property do not sell themselves. An agent is almost always involved. It takes quite a bit of time on the Agent's part to sell a house. They may show a person 10 or more houses. This will probably take an hour or so each (minimum). If they "sell" the house they have a lot of paperwork and hand-holding to do and then there is settlement. Needless to say an agent has a lot of time involved in each sales. They do this for 6% to 8%.
Traditional auction houses aren't usually in the 25% commission range. More in the 10% to 20% range. Only high-end, VERY specialized auction houses can get a 25% premium. Auction houses have expenses not incured with domains. They need physical space to store the merchandise. Sometimes this is very expensive as they need climate controlled environments and massive security to protect the merchandise. They pay pretty hefty insurance rates also due to the fact that they have such expensive items there. None of this really applies to domains. They don't need special environments, you can store one or 1 million domains in the same amount of "space". There isn't specialized, high priced insurance needed to cover things like water damage, theft, etc. No security is needed to protect the items, etc...
Saying 25% is charged by these premier houses isn't really true. Some items yes, but most things they sell aren't at this level. They also (at least used to) use a sliding scale so that the more the item sells for the lower the commision is ie. 25% of the first $25K, 20% of the next $25K, 15% of the next $25K and 10% on anything else. <-- made-up illustration on tiered commissions.
Traditional auctions also have different obstacles then domain auctions. Besides physical space to store the items, there also needs to be "viewing rooms" and security setups and security people. Buyers want/need to see the items before they purchase/bid on them. Only so many people can look at an item at one time. There really is no counter part to this in domains. If you have the domain list ahead of time you can determine the value yourself before the auction. There is nothing to "see" per say at the time of the auction.
You can sell more domains in a given period of time then any normal auction item. You certainly can sell a whole lot more domains then houses in the same given time it takes to sell a house. These don't need to be $100K sales. 20 smaller $5000 sales add up to the same amount.
IMHO, it is deceptive to do the comparison to premier auction houses as they have FAR more expenses. They also have a long, long history that distinguishes them from every other auction house. Something no one (including Moniker and Sedo) in the domain industry can even come close to. One of the reasons people use these "high-end" auction houses is because of their staff or PR guys. The PR guys see certain items and make lots of calls and visits to existing buyers. They work hard to make sure the right people are at the event and interested in the item! They do a tremendous amount of hand-holding and kissing. They put politicians running for election to shame with their people skills. This part CAN NOT be underestimated and is why people use them at these high-end auctions. They do a tremendous amount of work before the item ever makes it to the auction. This just does not translate to domain sales at this point.
If you were to "try" and model domain sales after these premier auction houses and take all the expenses into consideration and then base your commission scale on top of their model you would probably be setting commissions in the 5% range and certainly no more then 7% to 8%. A sliding scale of 8% to 10% (and dropping based on tiered sales price) would probably be more in line comparison wise.
Having read this, I'm not against Moniker taking a 15% commission. We are all capitalists! I just wanted to point out that everyone is comparing apples to oranges and there is very little basis for doing this once you "truly" understand everything involved in the process of high end auctions.
My $0.02,
Carlo