The Winchester/Ithaca fans almost always fall back on the "machined parts" as a key point in their arguments. I am sure many of them have a small machined alter somewhere in honor of that point. But, a whole lot of people - including me - only care what they look like, feel like, and how they perform. The Remington 11-48 ushered in the era of truly interchangeable parts and the 870 was a direct beneficiary of that development. The 870 proved itself to be just as serviceable and reliable as either of the other two, and offered the flexibility of inexpensive extra barrels that could be swapped by the owner in minutes in the era before choke tubes. And, since it could be manufactured for less money, it sold for less money. Many other gun companies jumped on the bandwagon of stampings as an alternative to all machined parts, and greater clearances to allow interchangeable parts, but they learned it was not as easy as they thought. Fortunately for those who love Wingmasters, Remington got it right the first time and never looked back.
In the hands of a good shooter, there is no difference in the guns' capabilities. I am sure with a little practice George Digweed could pull off the same amazing shots with any of them that he does with his preferred O/Us. The Ithacas were never targeted primarily at clay shooters, but both the Winchester and Remington racked up many wins before the O/U became popular. However if one breaks, the Remington is far less likely to need the services of a good gunsmith to get it running again.
The Winchester is gone. The Ithaca is barely hanging on, under the third different owner. Most of the nails were put in their coffins by Remington.