I don't find it ilegal at all. As mentioned by some, they are not claiming you can play like the athlete. They are just using the athlete's image to attract buyers. Just like clothes and food products...Lebron can't play like he does drinking Sprite all day, Jordan and Bird surely wouldn't have been able to move like that eating McDonalds and Lays all the time. And you know Gatorade, they have special formulas for athlethes not sold in stores!
I think that the issue is not with the PJs, the real problem is that companies don't continue of make available products that athletes use. The Head Prestige Classic, is an example of a racquet that should remain in production...there seems to be a wide enough demand, with most reviews claiming it to still be the most superior version of the racquet despite there being about 5 incarnations of it afterwards. Racquets should also be available to the public if an athlete uses a common though now extinct frame with a PJ...again pointing to the PC, if say Safin is using a straight up PJ PC, it should be still available.
However, custom made frames, are a different story, since it wouldn't be possible, it wouldn't be cost effective to try and make each frame variety.