The bug is that if you didn't hear the conversation you can still search the mono-rail and find the bomb. It simply shouldn't be there like a lot of quest related things and the rail just mysteriously explode.
It's bugged, and the two quests are linked, one bugging the other, making "No, Not Much" something you can't complete if you did "I Put A Spell On You" the way I did. Otherwise, if it was scripted and intentional, I'd get a Quest Failure notification for "No, Not Much". Hsu would never give the reinforcements, and so the quest is a failure. I'd return to Bitter Springs and my dialogue options would be along the lines of, "I tried, I'm sorry I couldn't do better." I don't even think I got a Quest Failure notification for "I Put A Spell On You". Not sure. I got paid and got XP, so it was a Quest Completed.
Having saved the monorail, I don't know precisely what he says to you. If he's just not sending troops, I think that's a mistake by the writers; he should say that he can't afford to lose any troops given what happened to the monorail, so you know the cause and effect of the situation. But it's still a very sensible mindset for him to hold.
He just says, "What on earth makes you think you can make troop deployment suggestions to me?"
I did the same thing , did all the quests I thought I could find for the NCR at McCarren (see spoiler) [spoiler]until I found the one for the First Recon in the camp right in front of the Airport terminal (the one for the tough chick) you need to talk to her commanding officer and you see what happened to her and how to help her.
I said above I completed the 1st Recon quests concerning Betsy.

I think that's her name. Tough lisbian chick. I took great pleasure in executing her rapist.

Being "Accepted" was enough for the other camps where I'd completed all the missions around the area. Also I asked for reinforcements when I was "Liked" earlier, but I picked up Cass as a companion and took the violent route in her quests, when I killed McLafferty my reputation with NCR was damaged and I dropped down to "Shunned" and worked back up to "Accepted." S'not the relationship or reputation, it's the way I completed the previous quest that's effecting this one.
- Cheers for the responses guys. :vaultboy: