The DSLR is made to match the human eye on earth, and unfortunately a sensor does not discriminate between NIR and visible photons. Anything with a temperature will emit black body radiation in the NIR and this is what the cameras filter is there to block (otherwise our photos would all look like they were taken from a COPS helicoptor), unfortunately the filter does not stop sharply where NIR becomes visible, and this causes low QE for the longer wavelegnths.
The human eye percieves red and blue relatively poorly as shown here.
http://en.wikipedia.org/wiki/File:Eyesensitivity.png