Bobby,
I used to believe that - but after my single leg flight from Copenhagen back to Biggin Hill, via northern Germany, Netherlands and Oostend about a year ago. I found that none of the appropriate ATC units had my flight plan, including Oostend who was a little unimpressed by the fact that I had not addressed the flight plan to them.
I also had a hiccup when flying from Brittany in France to Barcelona, where the ATSU had to search for the flightplan as it wasn't addressed to their respective military unit. I had assumed naturally that as my intended route crossed a military zone, that they would be given the flight plan, but they weren't. (again all filed through SD)
Technology is a wonderful thing, I too work in that industry, but it can occasionally fail (and often does too!).