tcpd, inetd/rinetd and iptables

What is the correlation between these programs? **tcpd** and **inted**/**rinetd** are very old but despite this they are still present in many distributions ... why? And there is also a correlation between hosts.allow and hosts.deny with **tcpd** but i noticed that these files are present even when **tcpd** is not installed ... (trying with the command **dpkg** also noticed that hosts.allow/deny is not correspond to no package) ... well .. a mess. Who helps me clarify? Thanks