There is a hadīth which I read somewhere that if a man approaches his wife with the intention of sex and the wife refuses, then angels curse that woman till daylight. Does that mean that a wife is never to say no to her husband?

All directives of the Qur’ān and Hadīth have common sense exceptions. The hadīth which you have quoted pertains to a refusal by the wife without any genuine reason. If she is tired, ill or is not in the proper frame of mind, it is the husband who should adjust to the situation.

The Prophet (sws) has on a number of occasions instructed husbands as guardians of their wives to deal very affectionately with them. This is what he said in his hajj sermon:

Take good care of women, for they are in your trusts and have no control of their selves. You have only taken them as a trust from Allah, and you have been permitted by the words of Allah to have sexual relations with them. (Quoted from Ibn Hishām's Sīrah)