Also, when the 1st funnel fell, Titanic wasn't only listing foreward, it was also listing to port, the direction the funnel fell. The list to port would've put undue strain on the starboard cables, causing them to snap. And I don't doubt that the water around the base at the time didn't help matters. As far as why the other funnels weren't seen falling, I have a theory.

---When #1 funnel fell, the lights were still burning as Titanic began her final dive. After the lights went out, just about anything could've happened that wasn't seen by the lifeboats (remember, it was a moonless night and after looking at the brightly lit Titanic, would have a moment or two of night blindness) including the breaking-up, falling of other funnels, etc... Even the survivors still on the ship and already in the water couldn't agree on what exactly happened. For example, Lightoller, who was in the water near boat B at that time, insisted that she sank intact. Of course, today we all know better. I'm sure that if Titanic had foundered in daylight, a lot more would have been seen that would've possibly been questioned to this day.