A regular user who happens to download less than $15.00 per month is not a fee-exempt user. They are someone for whom, in the words of the website, "fees are waived for that quarter."
[See this page and look at the questions "How much does PACER cost?" and "Can the user fee be waived?": http://www.pacer.gov/psc/faq.html ]
The Judicial Conference of the United States determines the PACER fees and appears to draw a distinction between the quarterly "fee waiver" available to all accounts and a "fee exemption" granted by a court after making the requisite findings (e.g., exemption is necessary to avoid unreasonable burdens and to promote public access to information, research is for academic/non-commercial use, etc.).
Sources:
Reports of the Proceedings of the Judicial Conference of the United States at http://www.uscourts.gov/FederalCourts/JudicialConference/Pro...
March 14, 2001: "no fee … [will] be owed until an individual … accrue[s] charges of more than $10 in a calendar year. … providing a basic level of public access consistent with the services historically provided by the courts."
March 16, 2010: "In order to encourage use of … PACER … by the public, … users [will] not be billed until their accounts total[] at least $10 in a one-year period. To increase the amount of data available without charge … users [will] be allowed to accrue $10 in free usage quarterly, instead of yearly, before they would be charged."
September 13, 2011: "… the current waiver of fees of $10 or less in a quarterly billing cycle be changed to $15 or less per quarter so that 75 to 80 percent of all users would still receive fee waivers"
September 23, 2003: "exemptions to the fee are only to be given upon a showing of cause, are limited to specific categories of users, may be granted for a specific period of time, may be revoked at the discretion of the court, and are only for access related to the purpose for which the exemption was given."
March 15, 2011: The Electronic Public Access (EPA) Fee Schedule provides for exemptions … upon a showing that an exemption is necessary to avoid unreasonable burdens and to promote public access to information. … [T]he Conference approved, a modification of the EPA fee schedule to include the following sentence: “For individual researchers, courts must also find that the defined research project is intended for academic research purposes, and not for commercial purposes or internet redistribution.”