what a pity....

Well, except from handling the protocol itself, TCP also require more sophisticated connection handling which all together make up quite a large ammount of code and tables in memory, so except from all hard work it would in the end leave less memory for the program/game itself. Taking the UDP road is not a bad choice for the C64 except from when its required to confirm to existing protocols (such as POP3, SMTP, TELNET, etc). But why would anyone want to do that anyway?

The COOLNESS factor!!!

You can actually do a UDP like TCP implementation, where you simply cut out all the crap that makes up the 'C' in TCP and just do an RST when something goes wrong, thus relying on the other ends hopefully more capable TCP implementation. This would of course cause some issues with C64 <-> C64 communication IF something were to go wrong... but then again, according to some, UDP across the atlantic works fine, so TCP without the 'C' probably would too.

Hmm.. wouldn't a RST abort (disconnect) the connection?

Indeed the Coolnez fact0r is never to be underestimated

What have I started?

Yes, but as I was trying to say.. It most likely would never do an RST unless the connection was really bad.
If it's for use with a custom protocol, like in this case with C64 poker, the custom overlaying protocol could just be designed to handle the possible connection loss. But then again.. why not just use UDP in that case ...unless you want to be able to play it from work and your company firewall doesn't allow UDP

poker .. hmm yes you have poker if you have irc thats how internet poker started
just a simple bot

just a simple gui on a irc showing the cards maby if you need

http://www.pokerfaq.com/irc_poker.html