I think a high score plugin would be useful.
Not all games require a high score table, but some do.
Just like some games don't require an achievement feature, but it somehow gets shoe-horned in and ruins the game (with trivial achievements like Mipey mentioned).
Those that don't want a high score table in their game, don't plug it in!
The plugin would have to be very customisable though.
If you can't get it to look and operate the way you want it to, you may as well write your own.