Allardyce said: "We could only afford James if we sold Roque Santa Cruz and I didn't want to sell him.
"He would have been one of the options had we sold Roque, though, and for three reasons. Firstly, he used to play for Blackburn and support them.
"Secondly, he's very experienced in the Premier League and, thirdly, he had a desire to be back in the top flight.
"Buying James and Matthew Etherington in the transfer window has paid major dividends for Stoke.
"James has scored some very important goals for them."