That's because Yankee fans, with few exceptions, have unreasonable expectations and think the Yankees have an unlimited pool of money, which 2012 demonstrated is not true. And as such, the Red Sox don't have an infinite pool of money either, and we, as fans, would be well-advised to understand the financial limitations of this team.
The posting fee issue is simple: It would be a one-time payment of around 60 million dollars. That is an enormous financial commitment no matter which team is making it. The key issue here is whether said financial investment would be sound, considering the fact that this team does have constraints beyond the LT limitations.
As an aside, i just don't understand the fascination with Tanaka. It would be cool to get him, but he's not as good as Darvish.