In addition to what Neil said - and which I agree with - valve spring pressures seem to play a part.
My old plow truck - '79 K10 with a GM Goodwrench FT crate motor - had no problems with any decent on-sale 10W30.
The valve springs on it were just the stock production stuff...stronger than a ball-point-pen, but hardly high-RPM stiff.
That said, the engine was probably from the mid-'90s era, and it seems likely now that quality control has slipped since then.