the reality in life is that all things flex. Nothing is absolutely rigid. thats Impossible.
When they stiff they mean stiff by industry std's or when judged against the competition.
XTR M960 cranks do flex a little, and thats simply because an infinately rogod material has not been invented yet.
Back to MTBR.com and the reviews.
Most reviews there are ridiculous anyways. What are they judging the components against, persoanl experience and that soretty subjective.
Also some of those guys I swear work for the companies of the components they review