I do not think Google, Yahoo, or any other company would be able to take more money away from parking because they feel like it. First off, they are a public company. That makes it a whole different ball game compared to a private company. They would have too much to risk rather than gain by stealing domainer money. I believe they do what they say.
Domain feeds at Yahoo, Google, and other companies are usually within the search network rather than the content network. The overall traffic quality scores on these feeds can range from 1-10, or Unknown (which is not enough traffic to determine a score). Revenue is determined based on this score. A 9/10 could mean a difference of 30% in revenue from 9 to 10. It depends on the keywords and ads that are being clicked on.
The decline in domain parking revenue does have something to do with economy, but the economy is not enough. We would actually be seeing the same, or even more revenue than before if it were just the economy. Take a look at Google and Yahoo quarter over quarter earnings. They are still growing even during this economy.
But anyway, the main reason why domain parking revenue has dropped is pretty simple: Most parking companies at one point or another used search partners (such as Ask.com) to display advertisements. Ask.com has a search feed (not a domain feed) that is from Google itself. The difference here is that a traffic quality score of 1-10 on their feed still gets you the same revenue. On a domain feed directly from Google or Yahoo, you are smart priced. On top of that, chances are Ask.com has negotiated a really good revenue share with Google, perhaps 80-90%. Maybe even above 100% if Google wanted to buy them out (there was a pretty intense bidding war against Microsoft and Yahoo so it is possible that it was a 100%+ revenue share just to get MSFT and Yahoo not to work with Ask).
Now, the parking companies that had the Ask feed were the following from what I know:
Skenzo
Parked
Bodis
ParkingPanel
ActiveAudience
There was about 20 or so total partners. On about March 1st, 2008, all parking companies lost the Ask feed, meaning they had to get a contract directly with Google, Yahoo, or someone else if they didn't have one yet. That is one of the main reasons why we lost a lot of revenue in the domain industry over the last year. With the Ask feed, parking companies were basically able to run mediocre traffic, and get paid top notch dollar for it, without any problems.
There are other companies that syndicated just like Ask. About 2-3 other companies, but they are technically not allowed to. As soon as their contract renewal time comes, I am sure we will see an even bigger drop.
I stand behind Google, and I think most of what they are saying, or all of it, is the truth. They are not stealing, they are just either a) smartpricing, or b) policing their partners as they should be from the very beginning. We were to be honest a bit spoiled by the revenues we received between 2006-2008. And now we are getting back to where we should be.
What the revenue everyone is seeing boils down to is the deals that parking companies have. All ads may look like Google or Yahoo ads, but they may be or may have been through partners with really good revenue shares and minimal restrictions. Google and Yahoo is policing their partners more than ever before, and a lot of these contracts are terminated, canceled, or expired without the chance of renewal in an effort for Google and Yahoo to clean up.