For most of us, we learned to use the word "Roger" early in our aviation career. We learned that it simply means that we heard and understand what the other person said. We were clearly taught that it connotes no permission or authorizations. For whatever reason, we then go through our career or hobby of flying and hardly ever use that word. And we seldom hear it spoken by ATC!
So what happens when we have a problem on the airfield and we tell ATC that we need to do something and they say "Roger?" What does that mean? Let me give you a recent example.
A C-210 received ATC clearance to taxi via Taxiway Juliette and to cross Runway 1/19. En-route, the C-210 pilot advised ATC that the aircraft just blew a tire. The pilot requested to exit the aircraft to inspect the wheel. The Tower authorized the pilot's request and asked the pilot to advise if he needed help.
At this time, a C-172 reported inbound with a request for full stop landings or touch and go's on Runway 1. The tower cleared the C172 as requested. (Can you see the Runway Incursion scenario developing?)
The C-210 pilot came back on the frequency stating he had a wheel come apart. The Tower asked his intentions, and the C210 pilot said if he moved the aircraft it would do damage and requested to go to an FBO. (Getting to the FBO from the damaged C-210 would require a runway crossing.) The Tower responded "roger." The pilot responded, “Thank you very much.”
The Tower then observed two men on foot walking towards the runway. The tower called the C-210 several times with no response. The Tower, after observing the men crossing the actual runway told the inbound C-172 to go around and enter right traffic for Runway 1, later changing clearance to land on Runway 5.
It appears to me that with the additional stress caused by the blown tire, when the pilot made his request to go to the FBO, he expected the Tower to give him a "Yes" or a "No", and when the Tower replied with a simple, "Roger," he forgot his early training that "Roger" is not an authorization -- and started hiking!
Fortunately, the pilot of the C-172 executed a proper go-around and landed safely on another runway.
The Aeronautical Information Manual is the authoritative source for proper aviation communications. You might want to take an opportunity to review communication procedures in the AIM: http://www.faa.gov/air_traffic/publications/atpubs/aim/. But most of all, remember your early training - "Roger" only means that someone heard what was said; it does not give authority to do something.
Remember that crossing any runway, whether in an airplane, a vehicle, or on foot, always requires a specific authorization from ATC.