I believe she did this because Harry had always gotten the girls in most of the books, and that Harry loving Hermione would be too predictable, Rowling probably wanted to do something out of the ordinary.
Ron Weasley's hair. JK Rowling said so in a webchat, I believe.
J.K. Rowling has expressed some regret over pairing Ron and Hermione together, stating that she maybe should have paired Hermione with Harry instead. She has mentioned that she believes Ron and Hermione would need relationship counseling to make it work in real life.
Harry falls in love with Ron's sister, they get married and Ron marries Hermione.
Hermione
Ron Weasley.
J.K.Rowling has stated many times that Harry and Hermione were never meant to be in a realtionship. In the final book she explains that Harry and Hermione are more like sisters. Hermione has always loved Ron and Harry has always loved Ginny.
Because Hermione belongs 2 Ron and always has loved Ron not Harry
Hermione Granger
Harry and Hermione were too close of best friends to be together. They need each other as friends. For example: The Half Blood Prince. When Ron and Ginny were with someone else they needed a friend(just a friend) to help each other through it.
Harry likes Hermione in the way that they are best friends. However, they were never romantically linked in any way, nor did one have a crush on the other. JK Rowling said she considered having them fall in love, but she decided Hermione and Ron were a better match.
Hermione Granger and Ron Weasley got married because they love each other.
Ronald 'Ron' Weasley.