Alas, they don't— you can easily demonstrate this for yourself. Startup an audio editor and generate tones at 25k and 28k (make sure you can't hear them— otherwise you have severe distortion screwing up your test) then play both at once. You will not hear a 3kHz tone.
The tone you get from an acoustic beat is not a real tone— it's a perceptual quark that requires you to be able to hear the tones in the first place.
I tried this in Audacity, with the project set to 96kHz and two tones at 25kHz and 28kHz. I couldn't hear either of the tones individually, but I could hear a tone when played together. This is on Windows 7 with the sound card configured for 24-bit/48kHz. Am I running into resampling artifacts somewhere in the chain?
EDIT: it turns out Audacity won't generate a tone above 20kHz (the UI accepts the value, but when you reopen it the value has been rounded down), so both of my generated tones were actually 20kHz.
The tone you get from an acoustic beat is not a real tone— it's a perceptual quark that requires you to be able to hear the tones in the first place.