Actually they just don't like it when you try to reverse engineer their games. Chat clients aren't reverse engineered it's something they supplied for the public a way to log in. Just telnet to uswest.battle.net (or any other subdomain) on port 6112 press control C and it gives you a login prompt. Note, I've had trouble getting this to work with other telnet clients but microsoft telnet works fine...

try it: telnet://uswest.battle.net:6112

Diablo 1 has been emulated but the only thing people use it for is logging on 500 bots which makes the server lag a lot more. Then they use these bots for channel and spam warring. If you think blizzard trying to stop that is lame then you must be a proponent of lag.

And despite what everyone is saying they are doing what they can to decrease lag and develope their games faster. They're hiring more game designers and doubling the power of all their servers. As well as upgrading the comps not just adding more.

Some links you might want to check out:

www.battle.net -Battle.net's official web site
www.blizzard.com -Blizzard's official web site
www.diabloii.net -A usefull site not just about Diablo II but a lot of blizz/bnet info as well
http://www.blizzard.com/jobopp/ -Job opportunities at blizzard
ftp.blizzard.com/pub/unsupped -Greetbot is a chat client that they wrote and released to the public TopazChat is one someone else wrote.

Well this is an update... they closed the chat gateway basically. You can still telnet in and use bots but they are restricted to certain channels. I guess it's to reduce lag they said it would be closed if abused afterall and I guess they consider it abused. =(