Every once and a while I come across beers that say they can be kept up to 5 years and become more developed over that time period, while other beers that are of the same style don't indicate this at all. I know that some styles are defined by how long they can be cellared, but for other styles how do you know? So my main question is:

What are the main characteristics that differentiate normal cellaring period beers from beers with extended cellaring periods? Does it have to do with the amount of hops? The amount of alcohol? The type of yeast? I'm thinking about trying to brew some beers with extended cellaring times and was just wondering what determines this.