I know the reasons for a differential unit on a RWD cars, and all RWD cars have it.

1.) But what about FWD cars? Do all FWD cars have differential unit?

2.) The Acura RSX Type-R has a LSD, but how does a FWD car benefit from a LSD?

Thanks

 

Yes, all FWD cars also have a differential, for the exact same reason why RWD cars have one. Also, LSDs are available for front wheel drivecars too. The benefits are exactly the same. FWD/RWD doesn't matter.