Actually, with the exception of DHS/Epcot, when you are speaking of theme parks, everything is really NOT relatively close together. We're talking miles apart. From the MK to Epcot is about 3 miles by the shortest route (which is the monorail; that track is 7.4 miles long, but it loops at both ends.)
MOST of the time if you are travelling in a private vehicle, the distance from on-site resort to resort, or from an on-site resort to a theme park parking lot entrance can be covered in about 15 minutes actual driving time. However, arriving at a theme park and riding a tram to the entrance turnstiles (or walking to them from a distant cab stand) will usually take that long again.
Travel time from anywhere off-property to theme park turnstiles will normally take at least an hour door-to-door at opening time. (The exception might be reaching DAK from the hotels near Sherberth Rd.)