I think Hasbro doesn't act on the 3rd party stuff because it doesn't really cut into their profits. The 3rd parties exploit the collector market and Hasbro's business model sells straight to retailers so there is no 'profit' conflict. If Hasbro decided to be more flexible and allow for collector centric products in a similar way like Mattel does within their business plan or if FanProjects begins to sell retail, then there would be a conflict but I don't see them doing that any time soon.
I agree however that the toys such as Defender and Collector and indeed intended to unofficially represent the Transformers characters but so far FP has been clever about it by making them 'similar but different' so legally they are unique toys from another company.
As it was discussed in the Unofficial thread, most fans would go for the official Takara-Tomy/Hasbro product over the 3rd party equivalent if they were comparable products. I know that if I had to choose between the Protector armor and MP Rodimus, the latter is an easy choice. Third parties exists because they have been successful at providing something that Hasbro has not by focusing on the neglected collector market. However I am sure that if Hasbro begins to officially release comparable products, the 3rd party would probably dwindle down to just simple accessory kits.
As an exaple, I am pretty sure that the new Wreckgar (assuming it actually looks like the Club Magazine photo) would be preferred to FansProject collector for the reasons stated above.