Been researching these for the past couple of months as well, here are my findings;
1. IMHO - flatbed cutters (Zund, Esko, Summa...etc) are one tool - and CNC routers are another. While both share some similarities and some similar functions each one has their own strengths and weaknesses and there is no ONE-SIZE-FITS-ALL option...you'll have to make a choice based on your wants/needs.
2. Flatbed cutters (Zund, Esko, Summa...etc) typically have a belt feed mechanism and drag feet that allows you to cut and finish roll stock (Poster, banner, vinyl, etc.) and automatically pull more from the roll with drag feet, whereas most CNC tables do not have this feature. (I think Multicam has the only one I've seen...) This makes them more suited for a digital print/sign shop that handles a lot of printing items that need finished. While it can "route" and has limited 3D routing capabilities, it really doesn't compare to a true CNC router's capabilities. See here:
https://www.youtube.com/watch?v=9D5Imikbf38
3. CNC Routers are for cutting parts/letters/dimensional signs in almost any material. Much more robust in build and higher power and strength for milling harder materials like aluminum, etc. They can be used as a drag knife cutter, but since most only have a fixed table, you would have to manually place each sheet of material or foam/PVC on the router to cut that way.
Just my .02¢