Access Control isn't my "thing", but from what I gather, your assumption is correct.
Previously, most access-control devices communicated over a RS-485 or similar bus. IP-based access control systems communiate over an Ethernet network, allowing you to more readily standardize on cabling, use commodity parts (switches, etc.), and do move/add/change stuff more efficiently.
Unlike cameras, where IP allowed for higher resolutions more easily, I don't think the average access control system suffers from a lack of available throughput, but I do think the RS-485 network concept can seem a little dated and harder to troubleshoot in a modern system.
So, (and again, I'm not an access control guy), I don't think IP-based access control systems open up as much new potential as IP-based cameras systems did, it's a little more of a convienience/standardization move.
Brian Rhodes would probably have a much better perspective.