I think such questions should be allowed. They have a factual answer (a list of all journals on a given topic) which may not be easy to find anywhere else. They also admit subjective answers, which would be short lists of the most useful/important/whatever journals in some area. The subjective answers are very useful since nobody could read all the journal articles about, say, numerical PDEs.
As discussed in this blog post, subjective questions can be very useful as long as people stick to answers based on references or on personal experience. Many of us have a lot of personal experience reading the computational science literature, and we can use that to give useful answers to newcomers or outsiders.
As Geoff points out, apparently SE staff have an aversion to questions asking for lists. But the stated reason is that such questions are really polls. That's simply not true in this case; take a look at Venues for publishing papers that emphasize softwareVenues for publishing papers that emphasize software. I learned a lot from answers to that question and I consider myself an expert on that topic. I'm confident that that information doesn't exist in any other single place. Indeed, I've been using that question to "show off" the site to many people, who have reacted positively.