People didn't say anything about KG and Allen because they were trades rather than free agent signings. Boston actually had to give up more than just money in order to get them. There were a ton of people questioning that move when it happened, thinking that giving up Jefferson and Green (along with everyone else, for all that Gomes was the only other player in that deal worth anything at the time) for a guy on the wrong side of 30 and maybe a championship was a really stupid idea. Miami didn't have to give up anything for this; all they had to do was not resign their expirings and they had the cap room.
Boston was criticized, however, for tanking the season prior, and there was a good amount of satisfaction across the nation taken in their landing the #5 pick. Of course, that has happened in this thread to Miami for this past season, so it works out.