Isn't the entier fs exposed as Z: or so in wine? I know there's some way to get to the user's home directory which is probably good enough to cause essentially the same amount of pain.
By default only. You can easily disable that. It always made me worried that anything in wine got access to my system, even though I normally wanted something closer to an isolated instance, so I always disabled that.
There may also be links to your home directory as "Desktop", "My Documents", etc. See winecfg for these. And note that your registry files may refer to Z: (mostly for fonts, it seems), or even directly to files outside your Wine directory.
If the software is Wine-aware, it doesn't matter. The \\unix\ filesystem namespace allows programs running under Wine to access the host filesystem whether it's mapped as a drive or not. And, of course, since Wine Is Not an Emulator, it could also use POSIX APIs or Linux kernel syscalls directly if it wanted to.
Wine is not an isolation layer. You can disable the Z: drive but the applications running in Wine still have about the same access a normal application has.
Most interesting. However, you have to butcher your system a bit in order to make that happen... That doesn't say there aren't setups like that, but they are really one out of million.