It would be interesting if Google released the numbers of how many people don't surf with 10 results as their display default.
This is going to make the impression numbers go up for those in the lower average positions - and I hope the normalizing formulas for Google about the min CTR are properly adjusted.
I counted them for my very specific three word keywords and there were 34 advertisers!
I typed in one general keyword.... and 94 ads came up! urg.... (my preference is 100 results, BTW.)
94 ads on 100 natural results.. It would be interesting to hear any feedback on this test.
If you refresh the SERPs, you'll find that the number of Adwords fluctuate.
This is due to a number of things. The two main ones are whenever you refresh or do a search with the exact keywords a 2nd time, AdWords goes through all the daily budget and inventory issues again to see what ads can be displayed.
Also, there is some 2nd tier formula which decides that if you've just seen a bunch of ads, and didn't click on any, then maybe the broad match wasn't quite what you were looking for and will display another set of results (this doesn't mean all the ads will be different, it just applies a different matching theme to some of the ads).