Shrink wrap is actually used a lot for environmental sealing on wiring, Raychem is one that comes to mind. Servicing means replacing the cable assembly, I do not picture a technician unwrapping the tape from the ignition system wiring to replace one bad cable.
http://raychem.te.com/documents/webservice/fetch.ashx?fileid=2438&docId=2196
In time and under the heat, the adhesive on the tape will eventually fail, I suppose for most who do not own the car longer than 4 to 6 years, it won't be an issue but it appears other Ford owners experience it sooner.
http://www.f150forum.com/f38/electrical-tape-88488/
Electrical tape is just basic cost cutting in my opinion, it's cheap, but there are better options out there like flexible plastic conduits and etc. that I have seen in other brands.