What To Expect With Planned VPS Downtime

I have several unmanaged Xen-based VPSes with a company that I've for the most part been very pleased with for the past couple years. I recently got an email from them saying that the physical server my VPS was on needed some components replaced and that the VPS would be "briefly unavailable" on a Saturday morning to do so.

Now, my definition of "briefly unavailable" is a few minutes, maybe 5 minutes max. I assumed that they would migrate the VPSes to a backup physical server while they fixed the other one, then migrate them back afterwards. In fact, I thought that Xen was capable of doing this in real-time with no downtime.

But the VPS was down for over an hour, so they obviously just shut down the box with the VPSes running. Because of the nature of my website, that particular Saturday was very inconvenient for me to have extended downtime. I was rather upset and contacted them to let them know, but they seemed rather indifferent and suggested that I look into upgrading to their redundant/failover services.

So my question is, am I being unreasonable to expect that *planned* downtime be limited to a couple minutes, or is it normal for companies to just take the servers down while they perform the maintenance? I thought that real-time migration to a different server was one of the benefits of virtual servers and I was surprised that they didn't take advantage of it.