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Unless there is a specific reason to keep the areas separate (e.g. you don't want people to be confused about the brand, or one activity is very inappropriate when paired with the other), it's usually best to keep the content on the same domain. brand.com/activity also usually looks more professional than exact-match-keyword.com. Furthermore, you often gain more trust when people see that the site's offering is well-rounded and includes a variety of activities. You can also benefit from accumulating good reviews from happy customers to just one website, rather than accumulating surfing holiday reviews for one of your travel sites, wedding holiday reviews for another and so on. Again, if you feel that the subjects clash badly and will create a weird user experience, you might look at developing different websites, but if you have a range of different activities / holidays that involve one location, I'd be 99% confident that these should all site on the same domain.

I noticed this as well but then some registrars do ask for special requirements. Check out the requirements on www.travel.travel: http://www.travel.travel/index.php/authenticate-register/industry-segments/