It is also possible for gifted children to have "asynchronous" or uneven skill development. (My teenage son recently laughed as he recalled how in kindergarten he could read the newspaper, but couldn't tie his shoes.) Your little boy's fine motor development is simply not yet caught up with his speedy brain. It is not uncommon after all, for four year olds to have trouble managing a pencil.
However, remedies for this problem are easy. Now is the time to improve his fine motor development. Encourage lots of building toy play. He likes to see how things are made, so encourage him to develop some of his own inventions with toys like Legos, K'nex, Tyco blocks, etc. Encourage writing play with crayons, thick pencils, colored chalk on the sidewalk, and so on. He can use little scissors and a glue stick to cut out words and make his own newspapers. Let him write shopping lists for you as he learns letters. Using thick clay will help strengthen his hand muscles. Have an art area set up and encourage him to draw something he has just learned or discovered. Remember, it is not unusual for children to avoid what is difficult for them, so writing play may not be his first choice. Please encourage it, however, as you are doing what's best for him in the long run. Good Luck!