And here begins another which is better debate.
My pennies worth:
The oils we use are a blend of chemicals and a good example is the need to switch based on a long-life or variable service frequency.
Meeting manufacturer standards 505, 507 and so on another way to show that oils differ.
Personally I'd use an approved oil like Fuchs Titan for £25 (currently), my car is my workhorse and anything I can do to make it's life easier and last longer is worth the extra. Personally I'd not fret about the small saving over the year for something so important. Only in an emergency I'd use cheap stuff.
The others to disagree should be along soon.