The issue with sliced meat is the meat itself...rots easily and is affected by the fact that it usually already has a high bacterial count anyway.
If you are going to the deli or coles, ask them to slice you fresh meat form the actually ham leg or whatever. The presliced meat has a greater surface area, ie EACH SLICE has 2 sides and the edge, whereas the roll of devon has only 2 sides and the edges, so the air cannot get to the middle of it (it will rot from the outside in) So the greater the surface area, the great area for bacterial growth and therefore the larger quantity of bacteria there will be iykwim.
Of course the other factor people do not tend to mention with processed meats is the processing itself. The more handling and mutilation of the core foodstuff (meats, ofals, additives, etc) the more chance there is for contamination at any stage of the process, be it all stages of one, if something is amiss at any stage, it will effect the final product...so the fod can be contaminated before the deli even gets it or touches it.

sort of like a fire there is an essential factor equation for bacterial growth...the equation works out to be something like moisture + air + heat + fuel = bacterial growth.

So that is why cryovacced food can sit on a bench or be stored for longer than wrapped meats - there is no air in there, so part of the equation is missing
Salting meats works to preserve them because it dehydrates, again removing one of the key factors for bacterial growth and survival.