Mr. Peel, the Reid role, can likely be played by a variety of actors, and I can easily see where Hammer would've brought a different, but useful young leading man quality. The decision to move toward Reid intrigues, since his known persona from his beloved TV series (wisely) has not been abandoned, and gives the Broadway audience a warm point of access. From the opening moment, the disarming everyman aspect of his characterization is recognizable and welcoming.
It's possible that The Minutes will have a long life, and like The Humans (which someone referenced above) will give a wide range of actors a chance at all of these roles. Pendleton is quite different from the Chicago casting, as is Brown. It's a testament to the play that its depiction of small town insularity opens the doors on how it's portrayed.
"I'm a comedian, but in my spare time, things bother me." Garry Shandling