Yes some of them are getting tougher. And at least one brand (I forget which) has an alegedly waterproof model. However, the general run of smartphones, the models that most people carry, IMHO are not as stout as a dedicated GPS.

Don't misunderstand me. I often carry my iphone (in a waterproof cover) when I go hiking. It serves as a back up to my Garmin, and I'm occaisionally surprised at where I can get cell service out in the woods. Note that I also carry a plain old fashioned compass and a map (in a plastic bag), which works even if the Garmin dies.

By analogy, I have a Leatherman, and it can be really handy in a pinch when I need pliers or a screwdriver. However, if I'm planning to do some serious mechanical work, I generally prefer to get my toolbox. By the same token, if I really need to worry about navigation, I prefer to use a tool optimized for navigation.