Check out the preamble to regulations regarding
Retirement Plans; Cash or Deferred Arrangements Under Section 401(k) and Matching Contributions or Employee Contributions Under Section 401(m) Regulations
published in the Federal Register / Vol. 69, No. 249 / Wednesday, December 29, 2004 page 78151
"The proposed regulations did not include any exception to the requirements for safe harbor matching contributions with respect to catch-up contributions. As part of the proposed regulations the IRS and Treasury solicited comments on the specific circumstances under which elective contributions by an NHCE to a safe harbor plan would be less than the amount required to be matched, e.g., less than 5% of safe harbor compensation, but would be treated by the plan as catch-up contributions, and on the extent to which a safe harbor plan should be required to match catch-up contributions under such circumstances. After reviewing the comments and the applicable statutory
provisions (including the amendments to section 414(v)(3)(B) made by the Job Creation and Worker Assistance Act of 2002, (JCWAA) (Public Law 107–147)), the IRS and Treasury have determined that no such exception is appropriate."
Basically, the safe harbor match applies to all deferrals and, the IRS having thought about it, decided not to make an exception for catch-up contributions.