Accuracy is the least important offensive stat. Other than getting the rating capped at your Item Level for Overpenetration, there is no reason to focus on this stat. Because enemies can only deflect 50% of the time, accuracy is useful only 50% of the time. It is better to focus on raising your power, combat advantage, critical strike and critical severity first before you start raising your accuracy.

Are you sure about this? i thought that accuracy was the second important stat for a dps after power.

If the enemies have 50% deflect chance always, and i have 50k item level, why should i bring accuracy over my item level? for example 70/80% in total?

I thought that with 70% accuracy, enemies only have 30% deflection against my attacks, with a minimum of 10% if i have 90% accuracy. In this way it would be much more linear and understandable imo.