TheLifelessOne, did you actually think before posting?
Firstly that was a battlenet 1.0 emulator client. We are talking about Battlenet 2.0.
Secondly the entire loggin system is different from battlenet 1.0.
Lets do some comparisions shell we...
Maps
1.0 - Downloaded via game host to players.
2.0 - Downloaded from battlenet to user.
Loggin
1.0 - Uses CDkey used to install game, unlimited accounts could be made with that key.
2.0 - Uses CDkey attached to your external battlenet account, all playernames link to that account does not matter.
Achievements
1.0 - No real achievements next to unlockable chat icons.
2.0 - WoW, SC2 and D3 achievements can be unlocked and attached to your battlenet account for all to see.
Map DRM
1.0 - None what so ever, the thousands of green TDs and LoaPs prove this.
2.0 - Handled by battlenet, preventing and possibly banning ill obtained or hacked maps and their authors.
Ladder match clients.
1.0 - Well I know little about this but all I know is it is rather simple.
2.0 - Auto player matching based on the WoW principle of leagues and points within them.
Singleplayer.
1.0 - Could not be logged into battlenet while playing singleplayer or campaigns.
2.0 - Able to loggin to battlenet account and then stay connected to battlenet while playing singleplayer so that you can chat with friends (well I can not confirm this but I guess it is prety obvious and certain as a lot of games have this nowdays).
Friend system.
1.0 - Finite friends list size, friends limited to same game as you.
2.0 - Multi level friends list with a lose list for aquatences you meet playing and a realfriends list for proper friends which lets you keep in contact with them no mater the blizzard game they are playing.
Chat (this probably does not affect the actual servers)
1.0 - Text only.
2.0 - Text with voice support.
As you can see the server software is totally different, if not totally new and made from scratch. Yes anyone who can code C/C++ could probably reverse engineer it but that will firstly take years and secondly it is highly illegal and will result in legal action (that has happened before).