This isnt wrong. Especially if you're just concerned with your own needs. Those are great pistols.
In answer to @
frozentundra's question: the 320 Pro series pistols are a "Law Enforcement" product line. X Carry frame, flat trigger, Hi Vis X Ray night sights, and an optic cut similar to the Glock MOS, or M&P CORE. The original Sig RX Series optic cut incorporated an integral rear sight on the plate, that came off with the plate. Due apparently to customer demand, Sig is going to incorporate the Pro optic cut system on their non LE products as well. The original cut was proprietary, and only acommodated the Sig Romeo and Leupold Delta Point optics. The new mounting system they are adopting will also allow mounting Trijicon RMR footprint optics as well.
Hope this helps. You're right, it is confusing.