@Psymon
First of all, IMO you can safely ignore Mark. He's probably very young, and clearly has too much time on his hands that could be better spent actually learning about the things that he babbles about.
That said, I think that you could use a little education, too.
I've been a UN*X user since ken got to Berkeley. I've been a WinDOS user since Ford Aerospace got 6 pilot-build IBM PCs running PC-DOS 0.96 beta (I fiddled with Vista for a year, but finally gave it up as a waste of time and space ... Not religious about it, I'll probably look at the next MS OS). I've been a Mac user since the first Mac came out (I bought one new, biggest waste of money I ever spent). I've been administering networks containing all of these OSes (and more) for a long time.
So, please allow me to address all your issues.
"centralised management, of which, Linux doesn't appear to have any. Ghost creates inflexible, static images"
I manage several Fortune 500 Linux networks from my office overlooking my wife's barn and jumping arena, here in Sonoma California. Remote administration has been built into UNIX-like operating systems from practically day one.
"Quick test here. You have 2000 desktops spread across12 physically seperate sites."
One of my smaller installs, then.
"If I have to perform any of the tasks listed below on an individual basis, It's a big fat FAIL."
Lose "fail" as a meme. It's very old and tired.
"Do not pass go, do not collect £200, and certainly do not win that big fat suppliers contract."
Monopoly? Are you sure you are a professional?
"If you make me physically walk over to any of the machines for any of these tasks, I will firstly set fire to you. I'll put you out when I get back, and the effeciency of the task will then be measured by the ratio of 3rd degree burns."
Threats? Over this kinda thing? Whatever.
"change the desktop wallpaper on either a machine or user group basis"
Linux, check. Windows, check. OSX, check.
"replace a peice of software on a group or all machines"
Linux, check. Windows, check. OSX, check. (that's "piece", BTW)
"add/remove shortcuts from whatever app launcher you may have"
Linux, check. Windows, check. OSX, check.
"restrict right to specific local drives by machine or user group"
Linux, check. Windows, check. OSX, check.
"modify the list of favourites"
Linux, check. Windows, check. OSX, check.
"modify the list of shortcuts on the desktop by user or machine group"
Linux, check. Windows, check. OSX, check.
"add an environmental variable"
Linux, check. Windows, check. OSX, check.
"restrict access to command prompt/terminal window by machine/user group"
Linux, check. Windows, check. OSX, check.
"add/remove favourites/bookmarks by machine/user group"
Linux, check. Windows, check. OSX, check.
"approve and deploy specific OS or software updates for all machines, and ensure they've all completed the update within a given timeline"
Linux, check. Windows, check. OSX, check.
"modify the file permissions for all machines local drives"
Linux, check. Windows, check. OSX, check.
"redirect the home folder to either a local or server share by user or machine group, or both"
Linux, check. Windows, check. OSX, check.
"change the proxy settings for a machine or user group"
Linux, check. Windows, check. OSX, check.
Looks like a wash, doesn't it?
But it's not. Given my background in all three OSes, I much prefer today's Linux, specifically the Slackware distribution, which I modify according the needs of the target user(s). It's faster, more streamlined, more secure, and it does everything 95% of all office workers need, without bloat.
The other 5% can have Windows, or OSX, or Solaris, or even a Mainframe if they absolutely need a specific software package that hasn't been ported to Linux. As I said, I'm not religious about it. Best tool for the job & all that.