^^^^You just kinda answered your own question.
"Nice way to make the match seem important."
I know the "nice" part was flippant, but it IS a simple way of implying further importance.
Why 'forever' doesn't mean forever? ....Just the way wrestling is, I mean, how often does "retirement" match mean just that?
Piper had a huge retirement match @ WM3 and returned. As did Mick Foley.... Given half a chance Flair will be back in a WWE ring before too long too. This isn't exclusive to WWE by any means. The only real difference is back in the day it wasn't so blatant cos the guys would often resurface in different territories. Besides, isn't it fun seeing how they write the guys back in (See Miz for example - Might not be saying much depending on what particular week it was, but that was the best segment on that weeks Raw.)
...Mind you, given age of the target market of WWEs current product, I doubt many of the guys and girls routing for Cena to 'bannish' Orton will be sat cynically thinking "Pffffff, they'll just draft him to SD anyway".