R.,
It is very possible that your boy is going through a growth spurt and is hungry at 4:00 a.m. It is also equally possible that he knows he gets your attention if he fusses. I know that "they" say that babies should be able to go all night without nursing/eating after a certain age, but I think that every baby is different, and if nursing your baby for 10 minutes at 4:00 in the morning allows him to sleep till 7:00 (and you to sleep too), I say go for it.
I had a not so good sleeper who woke up every few hours to nurse until he was 15 months when I weaned him.
My suggestion, feed him when he wakes up, but put him back in his crib. If it is the case he is hungry, he probably won't go back to sleep on his own, and he isn't rewarded by getting to sleep in your bed. I used to sometimes bring our son into our bed to nurse around 4:00 - he often woke at that time, and he continued to wake for it. Once I stopped bringing him into our bed, the wake up time got later and later until he was waking around 6:00 to nurse, still falling back asleep, and allowing me to get up and shower etc. while he slept in.
Best of luck!
J. - Mom to 19 month old Charlie and boy #2 due in a few weeks.