My Honda Pilot owner's manual states that I can tow a boat trailer up to 4,500 lbs. However, other trailers only 3,500 lbs. Can anyone explain to me why this is?

The 2008 Pilot has 2 trailer hitch capacities: 3,500 pounds and 5,000 pounds. The difference? For a capacity above 3,500 pounds, the vehicle MUST have an installed transmission cooler. If you do not, you will damage your powertrain. Check to see if you have the transmission cooler installed, and you will know what the towing capacity is.