I keep seeing people repeat this for some reason, but it's misinformation. Looking at any tile resource production tooltip in any of the gameplay videos disproves the claim that a pop's resource production is multiplied by its happiness value. Instead, there's a flat +10% production modifier above a certain happiness threshold (IIRC, most likely 70% - somebody helpfully provided a screenshot the last time we hashed this out) and most likely a -10% penalty below another one (probably 30%).
Good observation.
Did this change? There certainly seemed to be changes to happiness with respect to the agendas so there may have been some happiness balancing too?