I suppose it is conceivable that going 65 in the right lane when all the other right lane and merging traffic is expecting to go 70 or 75 could still be unsafe. If there's a big gap ahead of you and a long line of cars behind, it's probably a good idea to speed up regardless of lane (assuming weather's good and your car can handle it).
What's really frustrating and unsafe though is when drivers try to merge onto the freeway going 35 or 45 and traffic is going 70 in a 70 or 75 zone.
Several states have laws stating that slower traffic must keep to the right, but it's not necessarily dependent upon speed limit.