I've seen it in Miami quite a bit--you find somewhere "upscale" and they politely inform you that you have to be older to get a room there. 21 is typically the minimum age. But yes I do know what you mean--when an medium to large organization makes a collective effort (such as anime conventions, major LAN parties, many trade shows) that is typically wavered to an extent... usually because the convention chooses a venue appropriate for the attendees, so to seek out hotels that will rent to minors. Then again, most trade shows are centric around graudated and in-industry individuals, meaning that their venues are more appropriate for the older crowds--such as having CES being held in Miami.
