Shutter speed is an easy component of exposure to understand. Halve the shutter speed and you get half the amount of light striking the sensor. 1/50th on a small sensor yields the same amount of light per square meter as on a large sensor. The large sensor merely captures a larger area of it.
Field of view and aperture is an interesting component of exposure. This is why aperture is a relative size to focal length. If it wasn't, we'd need calculators in our pockets every time we changed it.
Imagine you have an aperture diameter of 5mm (78.5mm² area) and you increase your field of view by a factor of two (30º to 60º). This now increases the amount of light striking the same area by a factor of four (pi.R²), which would mean either your ISO would need to come down a factor of four, or your shutter speed shorten by a factor of four.
Now, if you keep the physical aperture size directly proportional to the field of view (determined by focal length & sensor size) you are cancelling out the field of view component. This is where the f-stop comes into play. All that matters now is the ratio. When your aperture is 1/2.8 the size of the focal length, for example, the same amount of light at a given shutter speed will strike the sensor regardless of focal length.
This means the aperture is getting physically smaller at wide angles (zooming out) and larger at smaller field's of view (zooming in).
How does this work on small and large sensors? Well on a large sensor the same field of view (cone of light) is restricted the same amount by the lens's aperture, but it is expanded to cover a larger are on the sensor.
ISO on the other hand is a standard. It determines a standard exposure at any given shutter speed and aperture.
Edited for clarification
The reason why a large sensor is able to produce a less noisy exposure is because the area of each pixel is larger (sometimes significantly larger). What this means is that the level of signal (light) compared to the level of noise hitting each pixel is greater. Think of it as a bucket of water with the same amount of soot at the bottom. A 5L bucket will have more water than soot versus a 2L bucket, increasing the usefulness of that bucket.
This is signal-to-noise ratio (SNR). On a point and shoot, the ratio of signal to noise is considerably less. Doubling the ISO for all intents and purposes halves the SNR. Because of these big bucket photosites on a digital SLR, ISO can be expanded considerably higher and still achieve less noise than a point and shoot, despite the same volume of light striking the sensor chip.
Phew. That's confusing stuff.