In that T&T case you mentioned, although finding out who the actual culprit is rather emotional, the thrill seems to wash over it completely. I remember, at the end of that case, I was just desperately caught up in the action and didn't have time to feel sad about the culprit. In fact, that very last piece of evdence you submit is just so thrilling, so "in your face" (is that a spoiler?), that I'm too excited to feel bad about it.
Most other stories, in their emotional moments, let you soak in the sorrow completely. They dwell on the sadness for a while and emphasize how bad the characters are feeling. Ace Attorney isn't like that. You're either too busy getting the bad guy or trying to ignore the sadness and be cheery anyway to actually feel emotional.
I think it depends on the person, then. I do find those action-packed moments from Phoenix Wright at the very end exciting, but they don't break the sadness for me. The "in your face" thing (nah, don't think it is a spoiler, and people who has not played it does not understand it, but clever pun xD) is afterwards followed by the breakdown of the culprit. From there you only hear the pointless taunt he send to you until he realize he's the one to blame. That was pretty sad. The ending for T&T was pretty sad, there was no cheer moment. Everything was beyond the point of any sign of happinness. Everyone had been betrayed by everyone by that point. And when you'd realize why people did it, it was even more tragic. Perhaps the game does not let you sink in the sorrow entirely because Phoenix tend to be (most of the time) someone who's not involved in the case, personally. He's the lawyer. He's the detective. He does not know the facts until investigated. The last case from T&T has several things to do with Phoenix as well.
I think that in the cases that Phoenix is not personally involved I would agree with you. There's sadness but there's no emotion, at least not coming from the main character. I would beg to differ when the case has Phoenix involved in it. The fourth case from the first game, the last one from Justice for All (which is also the fourth) and the last one from Trials & Tribulations are great examples.