Not only number of straps, but also type of straps. The key is that tri-shoes usually have one or two velcro straps. These straps stretch over time, making it harder to get a good fit. Road shoes often have ratchet straps, which offer a better control over your fit, and which do not stretch.
Yes, they are usually built on the same last and with the same sole. Trishoes occassionally have "mesh" or "water ventilation holes," but nothing that really matters.
But the construction of the upper can be quite different. Road shoes also usually have a more sung construction with a tongue and some more material, since they don't expect you'll need to put them on while riding. Tri shoes are usually more "open" for ease of entry/exit.
The upper on most, if not all, road shoes will provide a superior fit to that of a tri shoe due to differences in construction and more/different straps.
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