tk, A bit belated. Just to note, that the user interface may be object-like, and user friendly, without the operating system necessarily being object-oriented.
Applications and processes are probably left over from the old time sharing systems, from which unix is derived. There is no reason to organize the system in this particular way, except prehaps lack of imagination on the part of modern os designers. Also the notion of an application has strong favor with proprietary software companies. Kind of a little fortress seperated from the rest of the computer, which they can control, and resell to you and indefinite number of times.
Can't say an OO operating system is worth it. There doesn't seem to be any concrete reason to organize the system in this way except for the designers preference. New systems certainly have a lot of potential if only the hardware barier can be broken through.
If anyone is familer with programming the vertical sync interrupt of video cards, please contact me. I'm having a bit of trouble. This is a more modern card, the Matrox G400.