To correct Irina's reply - the CORRECT answer is:
Real estate websites (like Trulia, Zillow, etc.) have limited search filters because realtors own the MLS systems and have far more search filters on the MLS. Therefore, listings sent to 3rd party websites like Trulia do not have information for many categories because realtors REFUSE to give it to them. Examples include: HOA fees, property taxes, whether pets are allowed in condos or rentals, what is included and not included in HOA fees, etc.
Realtors hide this information because they want you and others to contact them so this way agents can recruit you to work with them. If all the "hidden" information was available online, then buyers, sellers and tenants would have less reason to call a realtor and of course realtors NEED you to call them so they can hopefully get paid by you.