This difference is due to backwards compatibility. Old Policy Server versions used these three ports for each service (44442 for Authentication, 44443 for Authorization, and 44441 for Accounting), however from R6.x version the Agents use the same port (by default 44443) for the three services, and therefore only this one is actually needed for the Agent to connect to the Policy Server. Actually, you can define different ports on the Policy Server only for backwards compatibility.
When you run the smreghost tool on a current version, you can only specify one port, like: <Policy_Server_IP>:<TCP_Port>, and the port is optional, so only to be used if you use a custom port.
smreghost -i ipAddress[:port] -u username [-p password] -hn hostname -hc hostconfigobject
-i <IPv4 address or IPv6 address enclosed in square brackets as in [IPv6 address][:port]>
-hn <Name for host to be registered>
-hc <Name of host configuration object>
[ -sh <Shared secret for the host> ]
[-rs] (enable shared secret rollover for host)
[ -u <Administrator username> ]
[ -p <Administrator password> ]
[ -f <File to store registration data in (defaults to ./SmHost.conf)> ]
[ -cf <Crypto FIPS140 mode (COMPAT or MIGRATE or ONLY)>
[ -cp <Name of crypto provider (ETPKI)> ]
[ -o <Overwrite existing Trusted Host> ]
So, if you want to enable R4/5.x backwards compatiblity when using a custom port on the Policy Server, you need to modify afterwards the SmHost.conf manually to reflect this and configure the three different ports, after registering the Agent with one port. If not, it is not needed because as mentioned, R6.x and higher only use one port instead.
If you are using the default ports, no ports needs to be specified when registering the Agent, and the SmHost.conf will be created using the three ports.