Apple Mail 6.2 doesn't download messages from Gmail over POP3
Review your settings on the Gmail website; could you have perhaps overlooked the checkbox to Download all messages from today on (or whatever your preference is)?  

By the way, I have my Mail.app accounts all set to POP3, and iDevices, of course, are on IMAP ... so that works; on the GMail page, you can leave them both on.

Check your Mail.app account preferences: in Advanced, the port needs to be set to 995. And have you run Mail's Connection Doctor, under the Window menu? When it can't connect, clicking on the error will take you right to the place in Mail preferences where the error is.