To be fair I've always lived in flats (above pubs) in rural areas with no fenced gardens. I currently live in a very similar situation. As a family we've had rescued adults and puppies in these circumstances and never had a problem with either house training or dogs going missing. It's all down to common sense and a part of that is ensuring you take on a dog that can fit your lifestyle. The other part is of course, accepting that house training a puppy in a flat does take more effort. You can't just open the door to your private garden in the morning. You should see the speed I can don jeans, jumper and trainers when I wake up!
When taking on an adult dog, you shouldn't expect it to act like a Disney film dog. It will take time to settle, and part of that is using leads and long lines until you're sure of each other and confident with recall and the like.
I was admittedly somewhat pee'd off with rescues turning me down (often rudely and abruptly) for not having a secured garden last time I was dog-searching, but having read Cayla's posts above I now understand why they acted that way. Having only ever enjoyed a secure garden once, for the space of 2 years, I couldn't really see the issue. I was of course working on the incredibly naive assumption that people wanting to rehome dogs were not utter morons, and were dedicated to the responsibility that dog ownership brings (regardless of extra hardships, such as never removing shoes for weeks because you're doing a marathon up and down the stairs with a pup in your arms every hour- or in my poor dad's case, a fully grown 6 stone Labrador who was initially terrified of stairs


).
Sadly people that look to rehome a dog can be just as deluded as those who want to pick up a pup from Gumtree. Such people can convince themselves that there will be nothing finer in life than ambling around the local woods, with their Husky off-lead, for 30 mins a day. Provided the sun is shining.
That was so much more of a ramble that it was meant to be

In essence there are a lot of idiots out there that make rules a necessity- rules that can seem odd to the sane among us.