Villa, who held the upper hand because Stoke were desperate to free up a loan slot, insisted on that condition remaining when the deal was made permanent in January.
"I just think it's the way football is now," said Lambert.
"Everybody tries to have every advantage they can to win a football match.
"Stephen obviously is an ex-player of ours. When he was on loan then he couldn't play against us. They took him permanently and that's just the way the jungle is and you try and win at every course."
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