Anyone can use "/tell @a Hello" to send private messages to everyone on the server.
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Maybe @a makes perfect sense, but it allows players to spam everyone with no log entries. Admin already has a hard time finding people who spam using clever methods. The @a selector just makes it even more annoying.
Also, things like @p[name=!myname] is very bad. Using certain /tell selectors enable players on a survival server to slowly pinpoint the position of other players. All selectors work, including x/y/z/radius. I don't think Any @ selectors should work for non-op. It destroys survival.
This is very much an issue, even in 1.7.4. It's now become impossible to play survival without risk of players or griefers finding out exactly where you are. It doesn't stop with @a, either. @r and @p work just as well. Players have been abusing this system to triangulate players using custom strings such as @a[x=0,z=0,r=1000] or @p[x=1000,z=-2000,r=100]. Using advanced trigonometry, a player can obtain the exact cords of a player in 3 whispers. Some players have been using it as "/me @p" to locate the person nearest to them, broadcasting it in public chat, or even using the more advanced aspects of the command to single out more specific players. What's one of the most annoying aspects of it is that in servers with many players, it's easy to spam chat and not trip the built in spam filter, or even avoid some scripts by either whispering a message using "/w @a @a" or sending a message in public chat by using "/me @a".
Someone from Mojang looked at this less than 24 hours ago and indicated that "this barely even rates" as bugs go. So I take that as in indication that they are not working on this anytime soon.
And @unknown, as wonderful as he is, primarily focuses on technical aspects like the rendering code, not gameplay. @Dinnerbone, @jeb_, @_grum, or even @SeargeDP all would have been better people to point such a question at.
You'll have to consider that people play Minecraft in a wide variety of ways, and that the way you play is not universal, not how the developers themselves play, not how many other people play, and thus not that big a deal to most of them. They may not really understand why this is a problem for you. It's probably not very high-priority, because it doesn't interfere with how they expect the game to be played. But tickets being marked duplicates of a private ticket strongly suggests that they're treating it as a possible exploit, even if it's not a high priority. The mods here have repeatedly stated that private tickets are only to be used for serious exploits or where personal information is at risk, and have changed the security settings on many tickets from private to public as a result.
So there's a strong suggestion that there's a non-high priority fix. But it's even possible that vanilla non-arena PvP is now not considered universally supported anymore. Yup.
It's funny because on my server, there are a lot of people who are lousy at direct PvP. So they use distance from spawn as their only defense. Those players are now totally screwed.
But I can see how this is an odd situation. Not a lot of servers out there do the anarchy theme with the Mojang server jar.
That's just what the
/tellcommand does.@atargets all players, so this behavior makes perfect sense.