I was always puzzled by this and experienced that myself. according to http://www.corrosioncontrol.net/motoroil_faq.htm
Are they talking about valve-steam seal? Also, I'm skeptical as most additives are very similar: ZDDP, Moly, calcium sulfonate, etc.
There is usually an increase in consumption after changing oil brands. In this scenario, it is usually only for a short period of time and then returns to its previous low level. The change occurs because motor oils differ in additive packages, which make up about 20% of the product. This change in the detergent/dispersant chemistry tends to remove previously deposited material that is helping to seal. Once this deposit is removed, the new chemistry will produce a deposit that regains full sealing benefits and controls oil consumption to the original lower level. Any increased oil consumption not related to these circumstances is generally due to a mechanical problem.