The graph below shows the average number of claims filed with each patent application. I used as my sample 400,000+ original published patent applications. "Original" means that these applications do not claim priority back to an earlier filing. The trend leading up to late 2004 was a very slight (but statistically significant) rise in the total number of claims being filed. Then, in late 2004, we see a sudden drop. Over a one-month time period, the average number of claims dropped from about twenty six claims per application to about twenty two claims per application.
The simple explanation for that change is that the Patent Office dramatically increased its prosecution fees. Instead of charging $18 for each additional claim (over 20), applicants who filed on or after December 8, 2004 were required to pay $50 per additional claim. At the same time, independent claim fees were also more than doubled from $86 per additional independent claim to $200. The PTO also began charging a hefty fee for patent applications that were exceedingly long. All these forces came together to give applicants a clear incentive to forgo potential claim scope in favor of reducing the up-front fees. Since January 2004, the number of claims has continued to fall slightly (but significantly).
This change is good. Applicants will tend to drop red-herring and worthless claims. That in-turn will hopefully lead to tighter prosecution times and more clarity of claim scope.