I think...
One of the possible reasons is a change in motivation. I never got into IT because "it pays well" but because I honestly think its a fascinating world. And that fascination goes /way/ beyond something as trivial as a choice of operating systems. Because all of them have interesting aspects (or plain out key strengths!) which can make working with them quite an interesting experience.
Do keep in mind that I reflect on this from a technical perspective; /not/ that of the end user who will happily start to panic as soon as their mouse suddenly stops responding... (I don't care if this is X or Windows).
That background has gotten me knowledge on stuff such as setting up a VPN connection between peers and then using GRE packets to tunnel all your data across it. Or knowledge as to why ksh doesn't fully supersede sh (Solaris/Linux). Simple stuff such as using ssh as a tunnel: "cat $file | ssh user@host "dd of=/location/file"". Or what about Windows? Nothing to learn eh; checking up if SpamAssasin is still running on my server, all I need is a mere prompt (on my box): "sc \\magi query spamd". But it also fuels interest in new technologies, such as PowerShell... Getting the latest 5 entries in the system eventlog on a remote server?
All I need is a mere PS prompt: "invoke-command -computername magi -credential sysop -scriptblock { get-eventlog -logname system -newest 5 }"
...btw; renaming the administrator (or guest) account on Windows is yet another insight which I got out of sheer curiosity and which can be quite useful.
Generalizing here: Take a new (modern) graduate with "extensive Linux knowledge". Most often he hardly has the amount of experience as your average Linux hacker with no "IT education" but 4 years worth of hacking experience.
What's that? Breaking into banks and defacing official websites doesn't count for IT experience? Well, if that's your thought then you've just proven my point for me. Look it up ;-)