A. Everybody has one engine that died of a horrible lube failure story, so the S-10 story doesn't mean much. Especially an engine that had seen a steady diet of quicky-lube service, an owner that didn't even check the oil with a blown engine, and a design prone to coolant leaks into the oil (pretty much all GM 60 degree v-6's). I've personally seen a Mazda where one of the quicky lube places left the rather hard to reach filter (a Fram) on for many oil changes, probably close to 20k. I've heard reputable accounts of "Caker-State", Mobil, Castrol, and Texaco causing engine failure...and frankly I'm not going to condemn any brand based on a few failures and a bunch of parts store hanger-flying.
B. Road Rage is right, Pennzoil has a soild product, in my oppinion their 15W40 is neck and neck with Delvac and Delo. The rest of their products are turning in good wear #'s too.
C. Oils do change over time! Fortunately, we have oil analysis, MSDS sheets, and standardized tests to detect when a formula changes. Examples here would be Castrol's (American) switch to Group III, and on the other side, the strong additive package in Motorcraft 5W20, or the switch to Group II/III basestocks in conventional oil (Chevron, Pennzoil, etc).