I understand your frustration, as you would like to know the addresses of all properties for sale. It helps so that you can make an informed decision. Most of the properties posted on Trulia are actually pulled from local Multiple Listing Services (MLS) through and IDX feed that Trulia has paid for and has signed a contractual agreement to use said data in compliance with the MLS rules. Some agents when listing property are instructed by their sellers to not disclose the address of their property on public internet sites, as they do not want public knowledge of that fact that their home is for sale (it might be vacant, and they are trying to avoid break ins, they may not want to have solicitation or junk mail sent to their property from services that scrape these addresses, etc.). Whatever the case may be, it is the seller's decision, not decision of Trulia or the Brokerage that has the listing.
When I list a property and enter it into the MLS, I have a box to check that does not allow the address of the property to be displayed on public IDX feeds sent out from the MLS. If my seller wishes for this to be checked, they sign a document stating to this fact, and then I check the box. The address is still available to Realtors when they login to the MLS, as these Realtors have signed an agreement with the local MLS, pay for access, and have a code of ethics that they adhere to.
If you are interested in seeing all properties available for sale in a given area, it would be a good idea to develop a relationship with a local real estate professional who has access to the addresses. There are many benefits to working with someone who helps people purchase property in a given area, and it will likely cost you nothing to work with them, as commissions are customarily paid for by the seller.
Best of luck to you, and I hope this answer helps shed some light on why it is not a game that is being played, but is in fact the right of the party selling the property to not have certain information publicly available on the interwebs.