This is 100% wrong and as much of a goalie legend as Dryden is, he knows less about modern butterfly goaltending than your average high school tendy. This whole "goalies drop as soon as you cross the blue line and never get up" thing is total bs.
Of course you want to drop FOR the shot when it's taken a vast majority of the time, but a large portion of my weekly goalie lessons (and I'd assume most others that are being trained as well) focuses on not only staying on your feet as long as possible, but also on recovering TO your feet as much as possible. Recognizing when you have time to get back on your feet and set instead of trying to slide around is an important skill to develop. Movement, balance, and positioning while standing are incredibly important and contrary to what seems to be popular belief, we are MUCH more vulnerable, and our options are severely limited once we are down than we are in our set and ready position.
If you meant that there's very little reason for the goalie to stand up for a shot then you're correct and I've misinterpreted you.