Well, the problem is that the receivers needs their DS flashed, so it's your friends who need to void their warranty and risk the ds being bricked... Also it's just much handier if it's not needed.
Also, how is the downloadplay compatibility with to a flashed ds actually? Are there any statistics about that?
Pfft, anyone who says the voided warranty is a problem has never actually had to use it. Nintendo doesn't check as other users have done warranty exchanges on flashed DSes. Same goes for bricking in the flashing process. If you bricked your DS, it is your own fault as you are incapable in doing so. I'm sorry you feel that way about yourself.
Everything works when a flashed DS receives.