Glass half full, glass half full.
No, this is different than glass is half empty vs glass is half full. This is the fact that people are clueless and instead of wanting to learn the truth they would prefer to be ignorant. Your reported capacity is changing, but actual capacity is not truly changing. SL isn't capable of adding back mythical space by formatting differently. Everyone is getting the 7 GB back from removal of PPC files. The rest is due to the way SL reports capacity. Hence, we read some saying 13 GB gained and others 25 GB gained, but that's just due to a larger drive will report more available. I will be done with this now, because it's apparent that people would prefer to believe that Apple has somehow improved formatting and is creating new space and improving a disk's capacity, in addition to removing 7 GB worth of PPC files, and that's their illusion!