Do switching regulators require a lot of external components to work?

I was looking at schematic of the DE2-115 Altera FPGA development board. The purpose was to look at example of how te power delivery system has been designed in it.

I found that they are using "LM3150 Wide-VIN Synchronous Buck Controller" which is a switching regulator to generate
1) 1.2V/5A from a 12 V rail
2) 3.3V/6A from a 12V rail

Also, they are using some linear regulators to generate:
1) 5V/3A from same 12V rail (using LMZ12003)
2) 2.5V/1A from 3.3V rail of switching regulator (using LP38692MP)
3) 1.8V/1A from 3.3V rail of switching regulator (using LP38692MP)

Now I have these questions:
1) The schematic page for the switching regulators is attached. Why do we need so many external components to make it work?
2) Why did they not find a more "integrated" switching regulator that will require less external components?
3) Why not only use linear regulators for all rails or only switching regulators for all rails?

1) 5V/3A from same 12V rail (using LMZ12003)

Click to expand...

This is not linear regulator. Read its datasheet.

3) Why not only use linear regulators for all rails or only switching regulators for all rails?

Click to expand...

Switching regulators are used for high power and Vout/Vin ratios, but are noisy. Linear ones are very inefficient for high power but no noisy at all. When you can use linear regulator, use it, because it is less noisy and also has less external components and is cheaper.

I experimented by creating switching regulators with a logic gate or op amp controlling it. The principle is to obtain 'On-Off snap action' in response to a changing voltage.

Example, suitable for low power only depending on type of op amp:

In general:
1) Because those particular IC's don't integrate those components - that allows more flexibility at design time
2) Integrated solutions may have a higher cost associated with them (though it depends) and can't be tailored to the exact power requirements as easily.
3) Switching -> Noisy but higher efficiency for higher loads. Linear -> Clean and simple.

That said these days I'm a big believer in integrated DC-DC solutions. I haven't done the math rigorously but I know our team doesn't have time to hand-design or tune all our POL DC-DC's.

Recently we've been using a lot of TI's LMZ series. As well as Recom's isolated and non-isolated LDO replacements. Several other companies have integrated solutions as well (Monolithic Power has caught my eye recently).