K.B.
Hi -
It very well could be simply his personality or he may just for some reason get embarassed when praised. That being said, my son was very much that way at your son's age and when he was 4 1/2 he was diagnosed with Asperger's. The behavior that you described on its own would not indicate Asperger's, however if in addition to your description above he displays some of the other behaviors included in the link below, I would suggest talking to your pediatrician about having him evaluated for Asperger's or other developmental delays.
http://www.webmd.com/brain/autism/tc/aspergers-syndrome-s...
Again, it is very possible that it is nothing more than a phase he is going through or his personality but the perfectionism and the problems with praise and recognition are definitely familiar to me in dealing with our son.
Good luck,
K.