I suspect the issue surrounds itself around the arbitrary number given to when lipids become a "problem."
In secondary prevention, (ie when you've already had your heart attack/stroke), reduction in lipid levels (irrespective of starting point) seems to reduce further events.
Primary prevention (ie preventing events in those who are otherwise healthy), does also seem to be supported by a robust body of evidence, although I'd be the first to admit that the tools designed to take into account other factors such as smoking, age, family history, blood pressure etc) are far from perfect.
But don't just take my word for it
CG67 Lipid modification: full guideline