He's right.
January is usually the coldest month of the year.
In December it can be warm enough to wear shorts outside, but you never know when it will get cold.
I went to IOA on February 2nd of this year. The low was 65, and the high was 80, it was a perfect day. Usually, temps are 60/75 in February, because I was watching it before my trip. The water was cold on the water rides, but it was ok. I had on two t-shirts and this kept me warm.
February/March is a great time to visit. Crowds will be very light. If you're going to DC, the water will be the same temperature no matter when you visit. Plus you'll have a wet suit on.
If I was picking a trip to DC, I'd vote for late February or March or even April just before spring break. That way the temps are sure to hit 80 and you'll be warm when you're hanging out at DC.
Here, try clicking on this page, it's what I do when planning a trip. It has the average temps for Orlando for all 12 months.
http://weather.yahoo.com/almanac/Orlando_FL_US_f.html