That's a bit of an exaggeration but SF has both weather and easy access to a lot of natural beauty, hiking trails, and so forth.

Detroit has a nice Riverwalk and I'm sure any locals can point to other local things of interest.

I will say that I was at a tech event in Detroit in the fall. Things I would do (knowing what I do about the city even today) in SF at night without a second thought felt risky and many other attendees felt the same--and there were some safety incidents. It wasn't even so much the things that might make you feel unsafe in the Tenderloin. It's that if you were walking 1/2 mile to someplace it was just deserted.