That's kind of to be expected though. They are probably looking for help on a specific subject, and so searching through postings initially related to that. Then they start browsing/exploring the site in more depth as they discover just what a vibrant community we are.
Those members who have been here longer will have settled into whatever niche they are most comfortable with, and I'm guessing pretty much stick in that particular general category or sub-forum, only ocassionally straying out into less familiar territory.
This kind of forum territoriality is an online cultural norm, and one which has been directly lifted from 'the real world' where we do pretty much the same thing across most social and business experiences. Take shopping for example. The first time you visit a new mall you will spend hours exploring it, popping into loads of shops and buying lots of stuff. As time passes your visits are better planned and you spend less time there in fewer shops and buying only what you came in for.
The trick is coming up with increasingly fiendish methods to encourage mall shoppers, and the same applies to forum visitors, to spend more across more disparate shop units... :)