I believe you are correct in your understanding of 2" and lower levels, "for it to matter as far as premature wear is concerned". A member responded, "That isn't true" which is another perspective. My understanding (opinion) is that the lower levels of one to two inches have your suspension components working at adjusted angles but are within the safe operating limits of the suspension components. Ball joints will wear eventually in a completely stock truck just as they will with a small spacer kit or levelling shock. We usually don't own our trucks long enough to see this. My understanding of the 2.5 and higher lifts is that you are reaching the maximum flexibility of your suspension components and anything other than smooth road surfaces will cause parts to exceed their maximum designed tolerances.
In my inquiries on this topic I have come across people in the business who will discourage any type of lift or level and are often equipped with some good horror stories. In shops where they do levels and lifts I have consistently been assured that I won't experience abnormal stress on stock components with a level under 2 inches. After reading and asking about this modification for the past several months I am going with a 1.5 level and am confident my suspension will remain as durable as stock.