I was just talking about this the other day with some co-workers. It used to be that you could manage your work network, even a decently large network, and know everything about it in your head. Reading a manual and being a smart guy (or gal) was enough to have a working environment.
No more. People expect remote access and that everything should be working 24x7, the added complexity of building out those environments, and the merging of multiple technologies means that every change becomes a much more complex endeavor. Encryption requirements makes everything more difficult to implement and troubleshoot. There are caveats with virtually everything, and I just don't have the time to be an expert on everything around me.
Example from this year - my IP phone system, which integrates with Exchange using custom nonesense for playback in outlook, using the LLDP enabled voice VLAN on my switches, with servers running on my vmware hosts, each of which have multiple redundant connections, with handsets connected to a switch using 802.1x authentication, that's complex enough as it is, but then buried deep in the release notes was a bullet point that exchange 2013 wasn't supported, 18 months after exchange 2013 was released. That's a lot of stuff to be an expert in; a far cry from 10/100 hubs with a single management IP address and a stand alone server that send voicemail over encrypted SMTP.