The really long post on the main page sums it up well, Perk is a terribly one-dimensional player at this point in his career, with any explosiveness that he maybe once had gone after the knee surgery.
I think both Danny and Doc saw the teams that would be in front of us in our quest to Banner 18 - Miami, Chicago, and to a lesser extent Atlanta, New York, Philly - and saw that none of these teams had a prototypical 5 that required a counter on our end. Maybe you could argue Horford, but he's a PF. I am not scared of Tyson Chandler on offense
The only team in our conference that has this guy is Orlando. But Orlando was collapsing last year, and completed the collapse this year. They were no longer a true threat. Also, Danny knew Howard was going into Free Agency either this year or next year...he might not even be in the Eastern Conference in 2013.
Our focus has to be on beating Miami, Chicago w/ or w/o D-Rose, Philly, NY, and Atl. We need long, athletic bigs who can run, catch Rondo passes, and hit open 12 footers. Perk has none of those qualities.