The main difference between what I did, and what the rest of my team did, was that I had the added responsibility for dealing with partners and vendors, negotiating contracts, scheduling hardware installations, and the like. The rest of the team was able to remain completely focused on the system administration issues that we cared about while I split my time.
For our team, it made good sense. For the other development/design teams, the way they're run makes sense. It all depends on context.