This is neither the law nor the actual practice in the US. It is just something crazy that DHS once said. If they ever actually searched someone 100 miles away from the border, that person could sue and there is no reason to believe that the verdict would be different from Almeida-Sanchez v. United States.
There are checkpoints a hundred miles from the border in many states and several videos of people suffering horrible results when they refuse searches at these checkpoints.
The TSA also routinely performs searches far from the border with their VIPR team. (because someone might drive a train into a building? http://en.wikipedia.org/wiki/Visible_Intermodal_Prevention_a... )
Here's a story from January 2013 http://abclocal.go.com/kgo/story?section=news/local/east_bay...
The most alarming part is how the "news" is now seemingly okay with all this.
Not true; this is absolutely the actual practice in the US. Look what you have to do if you want to avoid being searched in one of these rights-exclusion zones: