It really helpful to have developers know at least a little systems administration, and vice versa. When doing web development at least there's a fair number of problems that you should just let a web server, caching server, database server or even the operation system handle for you. If developers no nothing about systems administration they sometimes solve non-problems.

I'm just a guilty as anyone else in try to write code to fix a problem that's better handled by existing infrastructure and servers. I worked on a project to deliver invoices to customers in downloadable form. In the end pretty much very thing was thrown out and I just need to write the authentication part, because the sys admins pointed out that the existing StringRay boxes could handle everything else (http://www.riverbed.com/products-solutions/products/applicat...).

It's not that it doesn't make sense to have dedicated developers and systems administrators, as the developer you just need to know enough to be able to talk to and understand the admins position and thoughts.