Because so many times these days companies come out with games and then basically abandon them *COUGH* SPLINTER CELL PANDORA TOMORROW ON PC *COUGH*. It is nice that they gave us some new stuff for free.
And I think what you are thinking of is the new edition being sold... it comes with UT2k4 on DVD and a bunch of mods I THINK (I might be wrong). But it is nice that they made it available to everybody who already bought the game
.