After reading the page on Widmore, I came up with a theory that makes him a little more soft hearted than he appears. He told Ben that one day he'd have to choose between Alex and the island. Widmore already had via Daniel. Later in life he wanted to have children, but did so off the island in order to not have to sacrafice his child. As an older man he knew some things about Desmond, and wanted to spare Penny the heartache of losing him. He knew Desmond would have to choose between Penny/Son and the Island. Widmore sees the Island as a God; and thinks Des should choose/will choose to abandon Penny. Kinda sweet as a daddy. I'm not sure I would have done the same; but he was trying to be her protector and doesn't want to see his baby girl heart-broken.
Maybe this is a long stretch, but it seemed to flow with the summary of his info. page.