With the possible exception of Pro Tools (maybe not now that its gone native?) all modern DAWs use floating point math internally. What this means is, when the signal exceeds full scale it doesn't actually clip: instead the decimal point simply floats along a step, and the mix bus suddenly has room to accommodate it.

Of course, if you clip your main outputs you will hear it distort: your DAW needs to convert the floating point numbers back to integer fixed point to send it to your interface, and this is the point at which it will clip.

Don't take my word for it, try a simple test: import some audio (maybe rip a track from a favorite CD: doesn't matter really) and normalize it to full scale if it isn't already. Now crank the channel fader as far as it will go, so the clip lights come on constantly. Then bus it to a group or another channel, and do the same again. Carry on until you've boosted something like 48dB beyond full scale, and the audio sounds totally destroyed (you may want to turn your monitors down first!).

Now turn your master fader down to -48dB (or whatever amount you boosted by). If the signal doesn't clean up completely and leave you with a pristine normalized original it means there's a bug in your DAW and you need to switch to Reaper ;)