With all this talk about monitors here's what I can say.
As someone who has played numerous shows before I can say that yes, it is true that having good monitors does definitely make a difference, but I can't accept that as being any part of an excuse. Since I'm not a pro musician there have been plenty of times where I've had to play places with sub-par PA situations. In those cases there are some notes that are a bit off but as far as a point of reference goes, if you've done something repetitiously enough times there are certain notes that you can feel in your chest/throat as you're pushing that you just know are spot on by the way they feel coming out of you even though you might not necessarily be able to hear them.
For example, in another section on this forum I posted a thread with links to an STP tribute my band does on the side. In those clips we're playing a place that doesn't have the best PA setup where they had to turn off the stage monitors due to feedback issues with my mic. I know that throughout the set there were probably a few spots where I was a little flat but since I have repetitiously sung these songs in my life there are certain spots I can just feel in my chest/throat that I know are spot on and that's where I get my point of reference from. I know at least a few of you have seen these said clips and I've gotten compliments so I couldn't have been that flat. My point is that if I'm an amateur and I can do it fairly spot on for the most part with no monitors then a pro like Scott should be able to sing a song that he's been singing for 21 years without monitors with no major issues.
To further back up my claim.... Here's a video of Scott where he sings just fine by 2012 standards. Notice the first thing he does is he pulls out his RF in ear monitor. You'll see it dangling on his shoulder. He doesn't even need it. He is a pro who has performed these songs countless times and he is fully capable of doing it without an in ear monitor.
https://www.youtube.com/watch?v=K5XzZCfBLVISo Scott, Nick, the management, TMZ, CNN, or anyone else can tell me whatever they want but I'm not naive, I know what I'm seeing and if you ask me the main reason for this particular incident is definitely mixing booze and pills. Monitor trouble is just a side show.
Thankfully it sounds like it's something that was just limited to this one performance and hopefully the guys in the band have gotten through to him that this is something he can't be doing if he wants people to pay to come see him still.