I see that as a nice little tease to what could be in the future rather then a full on cliffhanger. I'm more then happy to see endings like that.That's what a good cliffhanger should do though. A shitty one that says "find out what happens next" is a poor use of the cliffhanger, a good cliffhanger should leave its self open, but also round off the story completely. I'll give you a fantastic example of a cliffhanger done properly - Metal Gear Solid -This raises questions, allows you to make assumptions, but also doesn't directly impact the previous events, but does leave its self open to expanding on what is already there. That's the sort of cliffhanger endings that work.There's absolutely no indication that series was going to continue, because it was resurrected years later, but they end on this massive cliffhanger where it's revealed that the President was the third clone. The last words are, literally, "Thank You, Mr. President."
I agree that Cliffhanger endings that feel more like "End of part one" can die in a fire though.