Only allowed 100 queries with relatedto? Despite using null and paginate false i can still only return 100 queries with this:

{% set results = craft.entries({
    limit: null,
    paginate: false,
    section: 'directory',
    relatedTo: relationParam
}) %}


How do I get all of them?

* UPDATE *

Well I found the problem and solution which is a bit strange - makes no sense to me.
I am passing relatedTo a merged string 'relationParam' which has the mulitpple categories I want to search for. Once I set the limits on the categories that are related to the entries -see below - it all works.

{% set c = craft.categories.group('locations').slug(countrySlug).limit(null) %}
{% set p = craft.categories.group('locations').slug(portSlug).limit(null) %}


So what doesn't make sense to me is that I am having to set the limit outside of the main entries query. I would have thought the entry limit specification would do this  not on the categories related.
The reason this happens is Craft has a default limit of 100 for all ElementCriteriaModel objects (this includes assets, categories, entries, tags, and users, also relations as you encountered). 

This isn't made terribly clear in the documentation, but you can see it under the defineAttributes() method on the ElementCriteriaModel class reference page.

As you discovered, adding a .limit(null) parameter overrides that limit.