I can see a reasoning behind going straight to lethal force with the bomb robot/drone (drone could be defined as any remote/autopiloted craft depending where you look). The criminal proved that he wanted to kill people and was very effective at it. He was still shooting and any of those bullets could have resulted in another casualty up to 400 yards away (to police or civilians). Police therefore had to take him out the safest and most effective way possible. Tasers, pepper spray, and other non-lethals I'd guess is maybe 50-75% effective. They are also effective for only a very short period of time. Someone would still have to take a chance of entering that room not knowing if the non-lethal was effective, and if they were still affected by it.
Police don't use non-lethals when they are faced with a deadly weapon (knife, gun, sword, etc) unless they have lethal force backup for those same reasons.
I'd question the police if they knew there were no other innocents and hostages in the room they blew up. Also they usually use snipers, I wonder why they weren't used.