Why so old? I recently had someone at work ask me why I would get a dog so old, although I suspect the question was really, "Why did I adopt an older dog again?"
Quite simply, I did it because they deserved a second chance, I wanted a dog, and I felt I could handle the challenge and expense.
Senior dogs do come with baggage, but honestly, some handle it much better than others. My pal Boo Boo, for example, was afraid of everything when I got him. I couldn't put my foot up to block him from going out the door first without him cowering like he was going to be kicked. For some dogs, trust doesn't come easy. It was probably six months before I noticed that he wagged his tail for the first time.
Patience is another big factor. Some dogs are stubborn, and none more so than some older dogs. I've been lucky in that once we achieved a certain degree of trust, that my dogs have had an open mind about working with me. It may very well be that older dogs are so set in their ways that they take longer to train, so patience is something that I've had to learn when dealing with challenges. On the dog's side, the biggest challenge would appear to be, at least from what I've read in the many ads for older dogs on PetFinder.com, is that they recommend the older dog, being an only dog. I could definitely see that and would never recommend dropping a puppy in with an old dog, who is more interested in sleeping than jumping around and playing all day.
That said, older dogs are frequently house trained, and are usually eager to please their new owners (at least in my case). With Rusty, this has translated into me teaching him a variety of new tricks and skills, the most important being "Leave It". We still have a ways to go, but with persistence (and the occasional treat... OK sometimes more than occasionally) he's learning all sorts of new things and is much less of the madman that I adopted.
As far as I'm concerned, there will always be an older dog in my house.