For good discussion I will include a counter viewpoint though I also voted to close some of the examples as they went against our stated policies. I don't nessesarily agree with these policies.
The way this site is supposed to work (for a particular situation) is as follows: someone finds or creates a puzzle for which he either does not know the answer or wishes to determine if others can find a superior solution. He submits the question to the site and recieves several answers. Based on the quality and cleverness of the answers (and several other factors) user vote on the best answer. Regardless of the votes, OP choses which answer helped him best in resolving the issue that brought him to the site.
If I found the inverted pyramid and did not know the answer, I cannot really improve the problem beyond the way it was stated in the question. A perfect answer would be the following:
"This puzzle plays on your assumptions that you want to retain the $100 bill but explicitly states that you are to remove it. The classic example is therefore to burn the bill. Several other solutions are convivable such as merely removing the bill slowly and relying of the force of a sharp pyramid to cut the bill."
It is worth noting that the only other answer given to the inverted pyramid question (cutting it) is likely infeasible so any solutions besides burning are debatable.
If the bottle/coin/cork question had said "you can't cut the bottle" rather than "you can't break the neck" I would not know any other answers than my accepted one!
The best example of this is the tiny man in a blender question. This was a famous interview question at google until it apparently was in that internship movie (didn't know that until reading your answers). I reallly would like to know what other answers are possible to that question that Google would have attempted. Only (really) two answers were provided to that question and there is not a number that should be consider problematic for this site.
Currently we average 1.6 answers per question while Area 51 claims that 2.5 is a good number.
I still agree that multiple answers to a puzzle is sometimes a bad thing. If someone says "I'm playing hangman and he wrote _ _ _ _ and I've not guessed yet; what is the answer?" that is a terrible question. If, however, someone asks a puzzle which is designed to make you cut Gorian knot, that kind of hits at the heart of the nature of puzzles as opposed to just arithetic or math.
The questions used as examples don't really have many non-trivial answers and can be answered reasonably easily. These should not be closed merely because they could have several answers as the Stackexchange system is designed to handle multiple answers with varying degrees of usefulness. This would cripple the usefulness of the site and prevent some interesting exchanges.
I don't enjoy they types of questions that are examples here but that does not mean they should be closed or banned from this site!