Similar code works for me:

var typeQuery = new ContentTypesQuery();

foreach (string type in SearchPage.ContentTypesCategories)
{
    typeQuery.AddContentType(type);
}

var accessQuery = new AccessControlListQuery();
accessQuery.AddAclForUser(PrincipalInfo.Current, HttpContext.Current);

var query = new GroupQuery(LuceneOperator.AND);
query.QueryExpressions.Add(typeQuery);
query.QueryExpressions.Add(accessQuery);
query.QueryExpressions.Add(new FieldQuery(searchText));

Hey, but is ContentTypesQuery a class of your own?

Haha, sorry. Sure it was. But it's a really simple class.

using EPiServer.Search.Queries.Lucene;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

public class ContentTypesQuery : CollectionQueryBase
{
    private readonly string AssemblyName;

    public ContentTypesQuery()
        : base("EPISERVER_SEARCH_TYPE", LuceneOperator.OR)
    {
        var assembly = this.GetType().Assembly;

        AssemblyName = assembly.GetName().Name;
    }

    public void AddContentType(string name)
    {
        base.Items.Add(string.Format("{0},{1}", name, AssemblyName));
    }
}

And the reason was that we wanted the editors to be able to chose which types that should be searchable.

I guess ContentQuery<SearchableSitePageData>() is implemented in a similar way.