Original Description:
Before the command system was rewritten in 1.3.1, /tell and all failed player commands would be logged to the console and server.log. This is no longer the case. All of these logging events can occasionally be somewhat spammy, but are always very useful to the SMP staff.

Additional Description:
Especially the logging of failed commands would make the life of Server-Wrapper-Programmers easier possible, who don't wan't modify the minecraft_server.jar but wan't to add new Commands.

Why whas this closed with "Won't Fix"?

The Solution:
The Solution for the logging of failed player commands is so simple!
At least in the MCP-Code the only change would be in CommandHandler.java in the executeCommand-method directly over the "throw new CommandNotFoundException();":

MinecraftServer.getServer().logInfo(par1ICommandSender.getCommandSenderName()+" tried command /"+par2Str);