We had a 20's 43' dragger growing up, iron bent over nails, by the 70's she was held together with spit and bubblegum, But Sears Oil based trim paint made her shine by the early June launching. It certainly was perfect for her, by the mid 80's good ole latex house paint worked just as well.
The original question was what is the difference between house paint and marine paint.
Technically, it has been answered. The final acceptable finish and longevity, well that's totally up to the user. I've owned the 20's dragger, the 50's Chris Craft Cruisers x2, and my current Mainship. Depending on the vessel, the type of construction, and the finish desired, it's all up to the user!!!