It's very well possible but I wouldn't place a wager on it. Portugal had a much better side in 2002 compared to 2014 (bascially not a one-man show) and the US is deeper in 2014 than in 2002.
I have no clue about Ghana. Gone are the likes of Appiah, Muntari, et al, and Essien is a shadow of his former self. What else do they have these days?
Stopping Ronaldo is the task. But if the central defenders struggle per usual and Klinsmann insists on midfielders as fullbacks, it may be a very long day for the US (and Ghana) against them.
I really have no confidence in the African teams. Their star players are on the brink of retirement.
Cameroon: They've got N'Koulou and Chedjou as their center backs. Not bad but not great either. At left back will probably be Bedimo, some Lyon defender, and at right back I don't know. Nounkeu. He plays for Galatasaray like Chedjou and has filled in there but is essentially a center back (I'm basing this all on a lot of CL watching, wiki and common sense).
Matip is probably a midfielder since they've got two good center backs. He might also play there. What they have in abundance are defensive midfielders. Matip, Makoun, Mbia, Song, Enoh and more. That's really what they have. Center backs and left backs, defensive midfielders and forwards. None of their players, besides the 32, by then it will be 33, year old Eto'o is known for scoring.
Ghana: Very small squad. Inexperienced. Look better on paper than Cameroon with Gyan, Ayew brothers, Kevin Prince-Boateng, Asamoah, Muntari and old Essien. Defense is seriously lacking. Cameroons 2nd string might be better than their first.
Nigeria: I probably recognize the least players here. They've got a Kennet Omerou, a 20 year old Chelsea player with 15 caps. Ever heard of him? The only African team with a decent goalie. Like Ghana, no real defender to talk about. Seems like a young team. Young teams tend not to do very well in the World Cups. John Obi Mikel, Joel Obi, Emenike, Moses, Martins, Uche and Obinna are the players to mention here. Decent enough attack but not great.
Ivory Coast: The only team capable of getting out of their group imo. Only because there's no frontrunner there. Sure, Colombia is the best team there but they don't have any achievements that make them stand out.
Drogba is the obvious star player. A very experienced squad. Their running on the same fumes as they did last time. The Toures, Drogba, Kalou, Gervinho, Zokora, Romaric, Eboue, Kone and Tiote. Added Doumbia, Bony and Lacina Traore to that mix. Really the only place where they didn't need to improve. Way too many strikers.
You know what you're going to get with this team. No surprises. They can make it to the last 16 and with a luck of the draw, to the quarter finals. Wouldn't be on them. It's not a team I expect to see at the WC in Russia. They're whole starting lineup will be 30-37 by that time.