There are generally a few reasons engines burn oil.
wrong oil for the purpose.
worn engine
damaged cylinders or rings
faulty PCV valve.
cheap quality oil
but when assessing the cause, all must be considered
Most manufacturers look toward low viscosity oil for the cars to Get better mileage, flow easier in low temperatures and because its standard across a large number of environments.
But if you look at your book, you will see that there are different oils for different temps, and unless you are running in the negative temp range, 10w or 15w will suit most situations.
At the other end of the scale, when you get up around the 40c deg range, as we get in Australia, the 30 weights are working at their limit, especially cheaper quality oils.
40 weights fare better in these hot environments.
I use 10w or 15w oils in my petrol and diesel engines, I don't get as much oil in my catch can on my diesel as i did when I was using 5 weight oils. This would indicate, to me, that 10w is not turning to vapor as much as the 5w, and any oil that turns to vapors is going straight through the PCV valve through the engine and out the exhaust.
And all engines use at least some oil, it lubricates the rings into the cylinder, its a part of the process and without it, your engine would seize pretty quick.
But most drivers, and especially those who do short trips or who never get their cars up to a good high temperate (such as highway driving) would not notice this loss, as the oil is being replaced by the un-burnt fuel, water and other crap from the combustion process and it appears that the oil level never changes. In some diesels you have to watch this carefully because the oil level actually rises.
How much is too much to loose? How long is a piece of string? If you have smoke coming out the back of your car, can smell burning oil, have oily plugs or have a film of oil on the tailgate. I suggest you have a problem.
However if you have to add a bit of oil between oil changes, and you have none of the above, its just how it is.
I have been told Rolls Royce cars burn a fair bit of oil, and that its deliberate, to increase the longevity of the engine, but never having owned one, I cannot deny or confirm.
If you are concerned, try 10w or 15w, if it solves the problem, happy days, if not dig deeper.
Cheers