They do, actually. It's just that Uberti has a slightly bigger bore - about .454 Vs. .452 for Pietta. All in all, both Uberty and Pietta cylinders must be reamed for optimal performance.
You are correct, but a 5 min. job with a small file and some cold blue solution remedies that in no time. What is more important is that Uberti seems to use a faster rifling twist, better suited for conicals. General wisdom is, that Piettas are better suited for round balls. But, on my own 1858 Pietta I'm using a modified Lee ROA conical mold, shortened with about 0.07", but still longer than the 200 grain .450 Lee offering. I have reamed the cylinder to .453, so the smaller conical does not fit anymore like it should. It shoots like a dream - no sign of bullet tumbling, very good accuracy with max charge of 35 grains of BP... I have shot some pretty decent groups at about 80 yards with no problems. So I think that the rifling twist is more than adequate.
As you say, it's not common. And you have some Ubertis with grossly oversized dovetails... So I'm not quite sure which is better.
Indeed. Also, both makers use some type of polyurethane varnish for the grips...
In general, Uberti makes a better finished gun. But it's better only on the outside. Inside the frame, both manufacturers show the exact same POS level of execution... One more thing - about 4 months ago I examined two brand new 1860s - Pietta & Uberti. Side by side I could not tell which is which, except looking at the markings - both guns were equal in terms of fit and finish.