So many people keep talking about that this requires 4 witnesses, and one asks to bring some scholars who does not see this, ok I will give you some shortly.
First I want to discuss the case in Dubai,
in Dubai, and this is from many people living there, because they have many foreigners, and those foreigners are accustomed to pre-marital sex, they have a lot of people committing adultery and when they get caught, they say we were raped, this is why in Dubai specially, they require very thorough investigation of the case to prove what happened.
Now to what Islam has to say in the matter:
If the guy was proven to have raped her, and he used a weapon, whether there are 4 witnesses or not, he takes the punishment of "Moharab" which is a someone who fights Islam, and gets on of punishments stated in Surah Maeda, Verse no 33:
1- Death Penalty 2- Crucifixion , 3- Cut their hands and legs, 3- Banished from the Muslims land.
All this after paying here "Mahr" which is marriage money,
If he was not using a weapon, he gets the adultery punishment. (which is lashes)
Now to the Scholars:
- Imam Malik "AL- Mawte'" (2/734)
- Sheikh Soliman Al- Bagy "Al Montawa Sharh Al Mawte'" ( 5 / 268 ، 269)
- Imam Ebn Abd El - Bar "Al Istithkar" ( 7 / 146 )
Why would she be punished if it cannot be proven?
This is a very serious accusation, and proving here does not mean merely DNA, DNA only proves sexual intercourse, but not rape, they could have just had sex and she wants to get at him for some reason, and because his punishment is so hard as already stated, it needs to be proven thoroughly, and if the accusation was not proven to be correct, and she was proven to have had sex, then she and him get the adultery punishment.
EDIT
Apparently and this is so sad, actually proving that rape happened turned out to be quite difficult, and in many countries the guy gets to walk away or the victim never reports it.
EDIT 2
They will both be punished if rape couldn't be proven but they were proven to have had extramarital sex.
Hope that answers your question.