There's a number of reasons why these cars use oil. It's not only the rings, but the OEM S-series cylinder heads also had rubber valve stem seals that wore out by around 80k miles. The replacement Federal Mogul parts use DuPont Viton in the seals, which virtually eliminates them as a source of leaks. The valves and valve guides also are not that great and can cause oil issues as well, more so with stock valve seals. This is often why you see more complaints about DOHC motors using oil than SOHC motors.
The pistons themselves were never made with oil drainback holes. They had 'oil reliefs' casted into the sides of the pistons, and as stated, they often got clogged up with varnish and carbon deposits, leading to stuck rings. All aftermarket pistons have oil drainback slots.
Even with a good valve train and aftermarket pistons, sometimes they still use oil. I'm breaking in my dad's 96 SL2 right now with a motor I assembled. It has probably the best valve job I've ever seen on a Saturn cylinder head, Viton seals, and Sealed Power stock pistons. Granted, I did re-use the rings because they were still 'new' from the last time I rebuilt his engine. The rings are Sealed Power and measured within the OEM gap specs. After 1500 miles, it's used a quart so far.