Part of the reason people are so confused about motor oil deposit causes is that there are a lot of myths about specific types of oil. One of the most prevalent is that paraffinic oils are a leading cause of deposits because of the natural waxes these oils contain. This belief does have an element of truth, so let's examine the makeup of natural oils.
Crude-based (mineral) oil is made in an oil refinery from natural resources. Crude oil provides the components for all oil-based products, including mineral motor oils. At the refinery, the crude is broken down into different components (like gasoline and kerosene); motor oil is only one of the end products. Crude oil is extremely valuable because it's a non-renewable natural resource -- when we run out, it's gone for good.
The term paraffinic (paraffin-based) describes a type of crude oil. Motor oils made from paraffin-based crude have a reputation for causing deposits in the engine, because wax is one of its major components. However, oil manufacturers remove as much of the wax as possible during the oil refining process, since the wax offers no benefit to motor oil, but it's valuable for making other products.
That said, some wax does remain; it's simply too expensive and inefficient to keep re-purifying the oil to remove all possible traces of paraffin. For a relatively inexpensive mass-market product like motor oil, it's just not worth it. So, the paraffin-based motor oil on the store shelf will contain minuscule amounts of wax. It's true that, at low temperatures, these small amounts of residue can clump into crystals, but this is far from the catastrophic greasy deposit-forming coating that many people fear.
Now that we know some of the downfalls of crude oil, you might be wondering about your alternatives. There's always synthetic oil, and though the name just sounds cleaner and more scientific, it might not necessarily solve all your problems.