Simply put, travel ball will not make those without innate ability have the innate ability.
I agree there are those early bloomers that are studs in the early years who become average or below average by 15-17 years old.
That being said, the extra reps and potential better coaching can do the following:
1) help the player with less than stellar athleticism learn and aquire more sound fundamentals. They will also gain more baseball knowledge and instincts by pure game experience.
2) help the player with innate ability to bring their talent to a higher level quicker.
As one of the other posters mentioned, many times HS coaches don't have the time or need to take on projects. If they have two kids with equal innate ability - one refined, one unrefined -they will take the one that is already refined. The other kid may not ever get the opportunity to refine his skills and show the coach what he really has.