Both the Motorola acquisition and the Waze acquisition by Google brought much slower approval processes as investigations took place. But, Microsoft doesn't have Google's standing in the mobile market, so its purchase of Nokia hasn't gotten the same scrutiny it seems. The Federal Trade Commission's (FTC) Bureau of Competition released a notification of the DoJ approval today, although the approval actually came through on November 29th.
In a prepared statement, a Microsoft spokesman said:
We look forward to the date when our partners at Nokia will become members of the Microsoft family, and are pleased that the Department of Justice has cleared the deal unconditionally.