I have always been confused by the sales engineer (presales) versus sales people, can someone enlighten me on what exactly are their roles - more specifically w

I have always been confused by the sales engineer (presales) versus sales people, can someone enlighten me on what exactly are their roles - more specifically why the distinction ? Here is what I know, at a place where I used to work selling expensive IPTV solutions (which was a limited market of big carriers - so I don't expect the sales people to be doing cold calls all day long), sales was apparently the place to be in terms of salary. The presales people were the more technical guys/gals who would get the customer requirements, help in the RFP, make presentations. And the sales people...well I dunno..I never understood why the presales people couldn't also be the full-fledged sales people closing the deals...I don't see the value-add...are the "sales" people there just to have smooth talkers who can close deals while pre-sales get the technical concerns out of the way ??