Reliable, in order UDP packets? with error correction? that's a great idea! lets do it!! oh wait...

no sorry sorry, my bad, just checked up on TCP. turns out it does that already *sigh*

nah seriously, there are advantages in terms of the routing of UDP packets and when dealing with a high volume of connections but using both TCP and UDP at the same time would give you far less headaches, send player movements and the such over UDP and reliable stuff over TCP. World of warcraft only uses TCP suprisingly and City of heros uses the tcp/udp hybrid method.