Craft entries related on a category page
I should note that the relatedTo method accepts a CategoryModel, not the title of a category. What you ended up doing works, but here's the way to do with the relatedTo method, which is what I'd suggest for anyone finding this in the future:

{% for entry in craft.entries.relatedTo(craft.categories.slug('your-cat-slug')) %}

You now have all entries that are associated with the given category, and can loop through them with the usual {% for entry in entries %} technique.

TL;DR: You can't pass the category name. You have to give relatedTo an actual CategoryModel.