The short answer is that POE gives you more options once you've decided that you want to write more than one-off IRC bots that don't do much more than IRC.
For example, pastebot and memephage are IRC bots that are also web servers. If you want your bot to respond on AIM or Jabber as well as it does in IRC, you can mix in POE::Component::OSCAR or POE::Component::Jabber. If you'd like to control your bot from a terminal, Term::Visual is an irssi-like console interface you can use with POE. POE::Component::Server::HTTP might be useful if you want bots with web-based control panels. POE::Component::Client::Rcon can be used to write bots that report game server status. Combine your bot with POE::Component::Server::IRC to use it as a bouncer, or maybe as a virtual IRC server that aggregates traffic on multiple channels. Use POE::Component::IKC::Server or POE::Component::Lightspeed to network many bots together, but only use these powers for good. Take advantage of POE's Tk or Gtk support to write graphical IRC clients. Or Gtk2, with or without POE::Session::GladeXML2 to automate the interface interaction. Bolt on POE::Component::Server::TCP so you can telnet into the bot in emergencies. Maybe you want to add POE::Component::SSLify to encrypt those connections. Create an IRC-controlled jukebox with POE::Component::Player::Mpg123, POE::Component::Player::Musicus, or POE::Component::Player::Xmms. Blah, blah, blah.
By the way, you should be sure to register a signal handler for SIGCHLD if you're working with child processes. If your zombies problem persists, and you're not just complaining for the sport of it, post a test case to POE's RT queue at rt.cpan.org.