I believe Tony was traded because if you look at the Patriot / Cardinal way on offense you don't need a superstar TE. Your big weapons consist primarily of a great #1 wideout (Randy Moss / Larry Fitzgerald) a decent #2 (Anquan Bolden / Joey Galloway / Greg Lewis) and a sold slot (Wes Welker / Steve Breaston).
Bolden was used in the slot quite a bit so it seems to me that the #1 and the slot are the most important in the passing attack. Also, they prefer a bigger blcoking TE for the running game. Tony was alright as a blocker but he was more of a third down / redzone receiving threat. I'm guessing but I think Pioli and Haley listened to the Falcon's offer of a second round pick next year and they compared that with the offense they are going to run and they made the trade because Tony wasn't going to be as big a part of this offense as he was in year's past.
Also, if you listened to the press conference Pioli stressed that he is looking at the 2010 2nd rounder as a bargaining chip for this year. Before we cast judgement on the trade we really have to see what comes out of it.
This definately reiterates that Pioli and Haley want guys that fit the scheme / system and want to be Kansas City Chiefs.