Yeah, the "lifetime" deal is probably fraught with conditions on both sides and the ability to cancel is given to both sides. It's really more a marketing thing than anything else, as evidenced by Agassi's and Sharapova's "lifetime" contracts.
That said, I think it should be noted that Federer could try any racquet and technically, Wilson could replicate whatever he wanted.
Wilson Six.One 95 16X18 Prince Original Syn Gut 17 @ 60
Strung Weight 358g 359g Balance 31cm 31cm