The 707 was introduced in the late 50's, the 787 in 2009.
Back when Air France 447 had recently gone missing, many were speculating that the aircraft had broken up in the turbulence associated with the massive thunderstorm it was flying through. Some aviation spokesperson, who I believe were associated with Airbus, said that the planes are designed to withstand the worst storms with a 50% safety margin.
Several airliner models from the 50's and 60's have broke apart in flight due to turbulence associated with thunderstorms (A 720 B, A BAC-1-11, and a F-27 in 1981). There were also breakups involving clear-air turbulence (707, Mt. Fuji, 1966, and a Consolidated Airlines F-27). I checked to see if their G rating was lower than the planes of today and they were the same - 2.5+ G Limit Load, with a 50% safety margin, so 3.75+ G Ultimate Load (beyond which structural failure occurs).
Why is this? Shouldn't the G rating be much higher if modern airliners are more resistant to violent turbulence?