I'd say Vista SP1 took the longest to install and that's already having the file downloaded earlier. I recall XP SP3 didn't take that long. With Ubuntu, the download from the server was the limiting factor. Otherwise, the updates themselves were pretty speedy. I downloaded again later and I got a steady 800kb/sec. So, yup. I take back that remark I made earlier.
But, hey. I grumble all the time when things don't seem right. But once things settle down, it's "Ooops. I guess I was wrong". Happens all the time.
Of course, Vista SP1 was on a laptop with a 4200rpm SATA hard drive. XP Home SP3 was on my main desktop pc with fast 7200rpm hard drives. The Ubuntu updates were from within VMWare Server of that same laptop.