I don't believe the story. None of these stories have panned out in the past, and I think it adds a whole other mess of issues. I don't think it's worth adding a BD drive JUST for games, and I can't imagine that they'll be able to get all the added BD functionality in an external BD drive (BD-Live, HD audio codecs, 24p output, HDCP issues, etc etc.) I mean I don't know how the HD-DVD drives handled stuff like that, but to me it just will add a bunch of confusion in the market place, and also Sony could use it as a way to leverage their PS3 (PS3 has BD built in while 360 owners have to BUY it separately with a bulky external drive.)
Adding a BD drive just adds confusion to the gaming marketplace, and the negatives associated with adding a BD drive in my opinion do not outweigh the positives, both PR-wise and cost-wise.