UPDATE: The 2010 Standards do not require detectable warnings on curb ramps.
The 2010 Standards apply to detectable warnings on developed sites. They do not apply to the public right-of-way. Scoping for detectable warnings at all locations other than transit platform edges has been eliminated from the 2010 Standards. However, because detectable warnings have been shown to significantly benefit individuals with disabilities at transit platform edges, the 2010 Standards provide scoping and technical requirements for detectable warnings at transit platform edges.
You may have been having problems finding the requirement for detectable warnings on curb ramps in the revised ADA/ABA Guidelines (published July 23, 2004). You won’t find it here.
But you can find it in the March 23, 2007 supplement at this link: Modification to 406 of Appendix D
406.8 Detectable Warnings. A curb ramp shall have a detectable warning complying with 705. The detectable warning shall extend the full width of the curb ramp (exclusive of flared sides) and shall extend either the full depth of the curb ramp or 24 inches (610 mm) deep minimum measured from the back of the curb on the ramp surface.