painandgreed said:
And computers use the same electricity and TCP/IP protocols. Programs are more like parts and accessories whcih are also proprietary and not available to all vehicles. The car analogy, although imperfect as all analogies are, is a good one.
The car analogy stinks

Well at least in the way you propose it here.
Maybe you are late in the game, but if you did own a Mac in the early 90s, it was a radically different beast:
- It did not use TCP/IP (you could install a TCP stack, though), but Apple had invented their own networking protocols - much more user friendly in a LAN than TCP/IP, I might add.
- It did use only proprietary connectors (monitor plug, ADB, NuBus, PDS) or high-end stuff (SCSI)
- The OS underpinnings were different from both the Windows and Unix world
- it was a truely different system.
Now we have:
- all networking based on TCP. Apple-specific solutions all culled and reinvented on a TCP base (Rendezvous)
- Cheap standard components with a platform-specific dongle (CPU). Gone are the days of crazy powerhouses like the IIfx and Quadra 840.
- They tapped the BSD world for their OS
While I don't deny this is mostly good news for Mac-users working in a colaboratory environment, it clearly shows how much of their R&D they have stopped over time.
And yet, the software issue is not really solved. Programs are nothing like accessories - I know more people buying Computers for the software they run than the hardware they run on. Just look around here: OS X is the #1 reason to buy a mac. For developers, things are different. You don't support a platform because you like its style, you do so because you like the business case you can make supporting it.
A lot of shareware applications are indeed like auto parts in the sense that every platform has a similar application targeted at a certain task. They are somewhat interchangeable. This is not, however, true for the big-boy apps like Word, Excel, Photoshop.
I have seen two technically superior platforms (Atari, Commodore Amiga) sink to their graves both because of management incompetence and neglect by thirdparty developers. Linux, the free juggernaut does not really catch on outside of geek circles not least because people don't regard it a serious OS as it cannot run business apps.
If you need car analogies to feel good, think about alternative designs that are constantly not catching on because of network effects:
Pressurized gas can drive a car and it is much more eco-friendly and could be cheaper. Almost no-one uses it because you have a hard time refilling outside of all but the larges cities. Biodiesel (harvested and processed from oil-generating plants) is not catching on because it requires a modification to the motor. Car companies could easily modify the motors from the start, but they don't because so few people would have the chance to use biodiesel.
To compare different brands on the fuel-gas platform (BMW, Porsche) is like comparing Dell and HP.