Force of habit
I usually post anonymous, force of habit.
You mentioned the list of monitoring apps but when I asked for a few examples you didn't give an answer apart from "Oh, there are loads of them".
I know there are loads of them, I know most of them can be scripted up and modified, If you want you could even write some scripts to pull it all together into one system.
I do not believe you can do all the above to the same level of quality without lots of faffing about. In your case you didn't mind the time expenditure, in my case I do mind. Give me a well integrated setup anyday...ok, usually.
The GUI: This goes back to the time / faffing around aspect but I highly doubt you could match their current GUI functionality without a very significant time investment.
I was going to list each point but again I keep coming back to the thought. How can you make a decent comparison without having experienced it from both sides?
We have used various unix tools (including tail!, sorry for not listing every possiblity under the sun), various open source apps (Nagios + plugins etc.) and we have also used this site (and scoutapp for other ones).
From our perspective this beats the previous setup hands down, and this is coming from a bunch who HAVE done both which was why I replied to your original post in the first place.