I can answer all of these questions/gripes believe it or not.
Film has always been widescreen because of the background shot. As others have already stated, like it or not the eye prefers a widescreen shot because it's more natural.... a horizion stretching wide in both directions with little vertical viewing.
Tv's were in 4:3 for so long because CRT tech makes it difficult to make a really wide tube (hard to shoot electron beams at such a sharp angle). Tvs were always meant to be widescreen, it's just the limited tech at the time combined with the added weight and floorspace (remember old tvs were huge) made it impractical. As a matter of fact, the first tvs were round, then 1:1 and gradually with got stretched to 4:3. 4:3 was as "widescreen" as we could get until projection tvs showed up, at which point we started getting 16:9 televisions.
Photography got it's unique aspect due to the typical subject matter. Landscape photography has always been much less popular than portraits. You have two portraits... a single person, with the camera on it's side, shoting from the hip up (most popular), or a group shot with a few people usually full length. In either cases, the 3:5 aspect frames suit the subject best, so that's how it evolved.
Computer monitors started as modified tv tech and they've remained so even to this day. This makes sense because several televisions are sold for every pc and it's easier to keep costs down if you can borow parts and manufacturing processes from tvs. For a while there monitor tech was ahead... we got lcds on computers first and it was 4:3 because that's what we were used to. Once flat tvs came out, however it switched to 16:9 becuase a manufacturer could make a really cheap lcd monitor by simply taking a lcd and stripping off hardware. In other words trends in computer aspects has virtually nothing to do with user preference.
Most people prefer a 4:3 screen simply because we are used to it, and 16:9 screens are new, meaning most websites and applications are still optimized for 4:3 screens. This will change over time.
Those that prefer a long computer monitor simply relate better to the analog model, namely a piece of paper. The size of paper, btw, has fluctuated much over the years as it was dependant upon the size of a US postal service envelope (approx the same width, three times the length so it can be folded into thirds) until the 40's-50's when office jobs became popular and the sizes of business paper became pretty much standardized.