1. A powerlifter arches to limit the range of motion needed to complete the lift. If you can decrease your motion it will give you a advantage to press more weight. The more inches you can add to your arch the less inches in your press motion. Most BBers don't care how much they can press focusing more on progression and muscle size.
2. Elbow position is key for a powerlifter also. Most BBers press with the elbows parallel with the bar while a powerlifter will pinch his traps and lats tight in and keep his/her elbows more tucked in to his sides. Also foot positioning may very. I have seen BBers pull the feet up on the bench to get the entire lift focused on the chest while Powerlifters utilize a ton of leg drive and really dig the feet in. And yes a lot of drive on your bench is in your legs believe it or not.
3. A lot of BBers use a pumping motion while they bench cause they feel lockout takes tension off the muscle. A powerlifter will mainly press to lockout cause every press done in competition must be locked out to be credited. This is why boards are often used to work the lockout with possibly a slightly higher weight than one can actually press.
4. Rep range will differ tremendously. A BBer will prefer to work higher rep ranges while a Powerlifter will prefer to work in lower reps and 1RM's pushing it more often. I've talked to many BBers who actually don't even know what their 1RM is they may just have an estimate. Most BBers think they would waste a workout if they don't get their reps in and reach hypertrophy while a powerlifter would think he wasted a workout if he didn't work heavy weight in triples and singles.
These are some distinct differences i could think of off hand but there are probably more if one thought about it longer. If i was asked i would say there is a big difference in the approach by each one but thats just my opinion.