Is Avoiding Fragmentation Worth It?

That is a business decision only you can make.


Obviously, some companies find it is worth the expense, others don't.

Sometimes even within the same company certain games are and others are not.


Is it worth it FOR YOU to do that? That is something only you can answer.

That increases your breadth.
The problem with PC games (indie anyway) is that you can rarely break even "out of the blue".
If you've planned ahead and made your code compliant with other platforms, you increase exposure. This has a cost, but generally, this helps you break even and snatch a little profit in the process.
Then again, there are extremely successful games on the PC that haven't ported to any other, so its entirely up to you, or, should I say, to your market researches.

Or just don't try to do everything from the get go. Choose a platform that you like, but code things in a way that will let you port your game to other platforms easily should you choose to do so in the future.