Vanilla Minecraft provides /w and /msg as aliases to /tell and /? as an alias to /help. However, these aliases are missing on CraftBukkit. While /minecraft:? is provided by /bukkit:?, /minecraft:w and /minecraft:msg are completely missing without plugins.

While this seems like it wouldn't matter too much, these commands are referenced from chat tooltips. While the tooltip for normal chat messages is disabled (normally it would be found by hovering over a player's name), these are still found in death messages and achievement notifications - clicking a player's name on one of those will bring up /msg player, which isn't a valid command on bukkit.

The easiest fix would be to alias /minecraft:w and /minecraft:msg to /minecraft:tell and /minecraft:? to /minecraft:help.

Wiki reference (note that it supplies both names for the command): /? and /w and /msg.