Scott- For uppers without any additional molding, yes you would see the dado on the bottom back edge of the stiles but you would have to be looking for it by sticking your head under the upper and looking up. Most uppers I have done recently had under cabinet lighting and therefore have an additional molding added to the bottom so it's nearly impossible to see the dado.
Bottom line is that (like everything else in woodworking) there are probably dozens of ways to construct casework. All of them will work and depend on what tooling you have available, how fast you want to build, skill level, and more. Can you construct cabinetry with just biscuits? Sure. Pocket screws only? Sure.
For me personally, I feel the dado/rabbet style of construction offers the best combination of strength, appearance and alignment/squareness in the finished casework. Until recently I didn't even own a biscuit joiner or pocket hole jig. I recently switched to using pocket holes for my face frames and I really like the results and speed, so I'll stick with that until something better comes along. The biscuit joiner I'm not impressed with. Maybe I am not using it correctly, but I find the play in the joint to be a little too much for my liking. I've used it for the last several cabinets I build specifically on the joint between the face frame and the bottom shelf of the cabinet. Alignment there must be dead on or you will have a lip. I'm just not getting it consistently with the biscuits so I'll probably go back to my old method of screwing a narrow cleat under the front edge of the shelf attached to the back side of the face frame. at least with that method I know I will get a tight seam that is perfectly aligned. A dado doesn't work here without a lot of extra work because of the face frame stiles.
I should also point out that my methodology is not substantially different than how I learned to make cabinets in the early 1970's in a custom production shop. So I'm old school for sure, but I have tried some of the "new fangled" technology. Some of it I like (pocket screws), some not so much (biscuits). I'm always open for better ways to build, would love to hear others thoughts & methods.