KN, you are probably hitting on the game's two "flaws."
1) When you fail a case, even after spending 20-30 minutes on it, you have to start back from the beginning. This is generally heralded as a flaw in adventure games - getting stuck and having to start from some point in the past. Sierra's games were notorious for this because you could miss one item that was later on irretrievable OR you'd do something wrong, which damned your chance at completing the game, but you wouldn't know until several hours later. Case in point: King's Quest 6, where you have to get into the castle at the end. There's two ways to do it, but if you attempt the first way and fail and then try the SECOND, by then you've basically screwed yourself out of winning. And that means, basically, starting over from scratch. It's the same in PW when you lose all your "points" during cross-examination, then being forced to wade back through testimony.
2) THere are times when you, as a player, are thinking "Wtf, I'm a lawyer, why not just question ____?" But the game won't let you, so you have to go through a lot of testimony just to hit back on the same question you asked yourself earlier, at which point you CAN ask it, and ultimately it progresses the case. I mean, there were times when someone said something weird and I caught it, but it wouldn't come into play until much later on the case. The whole time I kept saying "Wtf, they just said a HUGE contradiction," but there was no way for me to hit on it.
I.e., there's only one route toward progress. In Day of the Tentacle, if you can't figure something out, you can switch to the other characters and work on their problems. In the meantime, you might subconciously figure out a solution and/or run across an item that'll solve it. True, there's still bottlenecks, but at least you can busy yourself without a total stoppage point.
Problem 2 is less prevalent in other adventure games because generally there's little barring you from progression. For example, in Day of the Tentacle, you know you need to, say, get the contract signed in order to buy a diamond. There's only one way to do it, but the logic leading up to it makes sense inside the game world. Equivalently speaking, if the same were to happen in PW, you'd have all the necessary items and things, but you're still scratching your head because it ends up that something completely unrelated needs to be triggered first.
Good adventure games typically avoid these problems by providing clues from a variety of sources. Like talking to the same people, but using different conversation trees. Or asking other people, who might drop a little clue. Or being able to look at evidence and having your main character give you a clue. All of it is built around the idea that you can only move forward, and not damn-yourself backward. This is why I like Lucasarts's games over Sierra's, simply because the majority of the former's games do not create situations where you have lost, but are unaware. Sierra's are a total bitch because half the time you don't know you've killed your chance or winning and/or even with proper examination and look commands, you can't progress because you don't use the exact right word (Space Quest is especially guilty of this).
As long as we're on it, if you haven't already, do NOT play Sprung. The logic in that game is far worse. It's a nice little game and it needs more recognition than it gets, but the conversations are almost entirely nonsensical. I'm well aware that's how conversation normally is, but there's very little ways to determine whether or not you are doing something wrong without having to start over (i.e., problem 1).