Earlier this month WPP bought a majority stake in Acceleration, a 13-year-old consulting and services firm that helps marketers and publishers implement digital ad technology. (press release) The company employs 148 marketing technologists in London, New York, Buenos Aires, Cape Town, Dubai, and Johannesburg. AdExchanger spoke with Cameron Hullet, who leads Acceleration’s consulting and sales efforts.  As large advertisers re called on to provide?  Only a few years ago we were helping companies get the basics in place, typically around ad-serving, analytics and email. But the complexity of the technology stack has increased dramatically over that time, making it exceptionally difficult for any publisher or advertiser to keep…