Three key differences.
1- Monty and Dell want to assemble a contending, competitive roster by next season.
2- Jefferson fills a glaring area of need for our team (post scorer).
3- "Out with the vets" only applies to medicore veteran talent (i.e. Okafor and Ariza). I think we can all agree Jefferson is a much bigger difference maker than either of those two.
And come on, are you really making the argument that a 28-year old player is too old to sign to a 4-year contract?
My use of old was purely contextual. After all, Favors is only 21 and Kanter is only 20. Compared to those two, Jefferson is old. But compared to the average age of other NBA players, his age is optimal given the fact that the late 20s tends to be around the time when players peak.