Is it necessary to cook porridge (oatmeal)? It is possible to just eat porridge (oats) after soaking in water for a couple minutes.  

However, cooking it makes it creamier and softer.

I'm interested in knowing if cooking the oats actually changes them in some way (besides the heat), and if there is technically a difference between cooking vs. not cooking.  (e.g. is it the case that if I leave it to soak for a longer period without heating, it could achieve the same softness?)
Yes, there is a chemical difference.

When you cook the porridge, the starch from the oats thickens the milk like a pudding. You don't get the effect (propper name, anyone?) by just soaking them. Just as you will never get a firm pudding without cooking.

What you prefer taste-wise is a completely different question.