My biggest fear with a hosted environment in my line of work (Healthcare) is that if not done correctly with multiple points of connectivity to the world using multiple vendors, etc then the weakest link is your broadband connection. With a system in-house, whether it be PBX, VOIP or Hybrid, you can build in a bit more sustainability in the event you lose your broadband connection. Of course if our connection to the CO/dialtone provider goes down it's kind of a moot point, but the plan we are headed for right now is to have a Hybrid VIOP system that is about 95% VOIP, but has TDM phones in all of the most critical locations. So if the nurses desk has 2 phones now, one will be VOIP and one will be TDM even though the phones will look exactly the same. If we lose a network switch, or an edge router, or some idiot vendor wrecks a fiber run or whatever, those locations will still have service, and can call and be called in an emergency. Of course if the whole system tanks that will be a moot point, and if we lose connectivity to the CO it will be the same, but it does add a measure of redundancy, which, along with redundant critical electronics in the mix can help. We also have a WAN of sorts that connects all of our sites together, and each site will also be able to stand on its own if it loses the network connection to the mother ship.
In my humble opinion it's hard to do that with a hosted environment. In my town, with one primary last-mile carrier there are only so many ways to redundantly get service into our buildings without costly spending on special outside plant from additional vendors. Our city does have dark fiber plant in place, and we're definitely looking into what it will cost to use some of that for redundancy, but again, it will be quite expensive to roll it out....
I'm sure there are other companies thinking along that same logic stream, and I'm pretty comfortable that in-house equipment is still going to be around for at least the next 10 - 15 years, and at that point it will be time to look at the upgrade path again - who knows - it may be a completely different world then!