I'd say it's more that a rich person not signing up is expressing a strong preference against. For people who believe rich people are smarter than average this should constitute a substantial piece of evidence.

Imagine people buying a car where it costs $1,000,000 to change the colour. We conclude that anyone who pays cares strongly about the colour; anyone who doesn't pay we can only say their feelings aren't enormously strong. Conversely imagine it costs $100 to change the colour. Then for anyone who pays we can only conclude they care a bit about the colour, while anyone who doesn't pay must be quite strongly indifferent to the car's colour.