If what you said about SC's trial and error is true (I don't completely agree), then how come it's OK in Demon's Souls, which both you and Bebpo loved?
They are rather different, though, don't you think? What made Splinter Cell frustrating was the result of its stealth focus and the punishments of failure. As a stealth game, you are supposed to avoid breaking cover while covertly taking out enemies. Getting caught is a penalty, of course, but I found it particularly annoying in that it would ruin whatever you were attempting completely.
In a game like Thief or even Metal Gear, you had plenty of options available after getting caught that still kept the game flowing smoothly. The penalty in SC was too great and broke the tension. In a way, I feel that slightly less perceptive enemies make for more enjoyable stealth gameplay. While it was possible to take different approaches in certain areas of Splinter Cell, most encounters were clearly designed to be played a single way. Through fault of my own OCD while playing these types of games, I found that it just rubbed me the wrong way and lead to frustration. Mind you, I've finish the first and third game in single player, so it was not too much of a task by any means, but it was often annoying.
I'm kind of miffed that you would try to bring something like Demon's Souls into this, though. You're once again trying to make implications that my opinions on the two games are the result of my system preference. That could not possibly be further from the truth. My history with Splinter Cell goes way back before the PS3 was even a known quantity. The original was one of my most hyped games of its day and the subsequent disappointment left quite a mark. I ended up purchasing the following two games for different reasons. For the second game, the multiplayer drew me back in, while the third one seemed like it would address some of the issues (while also featuring a killer Amon Tobin soundtrack).
In regards to Demon's Souls, I'm not even a huge fan. I think it's a neat game that's very different from the norm these days, but I've not finished it. It is trial and error to a degree, yes, but it's definitely based more on caution and understanding of the mechanics than trial and error. Splinter Cell, as a stealth game, is very different in that you need to remain undetected to best clear a situation. Being seen in Demon's Souls was part of the game and dealing with those threats successfully rather than avoiding them altogether made it much more enjoyable. It is trial and error in the same sense as an old NES game rather than Splinter Cell. The slow paced design of Splinter Cell and its rigid structure made it tedious.
This has NOTHING to do with any sort of bullshit system wars.
Since when have casuals found bare-bones presentation, minimal combat and fairly high difficulty levels appealing?
Go look up some sales charts. The games have sold a lot of copies. I'm not saying Wii fans were playing these games, but I don't believe it's all hardcore gamers either. I'm sure a lot of its buyers were the same type of people playing Halo and Grand Theft Auto.