Yep, I've seen some people disable zoom in their webpages specifically to prevent Safari from auto-zooming all over the place as the user moves from this to that input. It gets really annoying if you have anything but the simplest form. And what webpage doesn't have at least one form on it, even just the search box?

I fully agree with OP that disabling zoom is wrong. I also think it's wrong for browsers to mess with the zoom level without the user's instruction.

Almost every weird workaround we still have today in webdev was originally written to compensate for inconsistent browser implementation of some standard. In the past, IE was the one that always did something weird. Now it's Safari. Until browsers stop trying to pretend that they know better than both the developer and the user, somebody somewhere will keep writing these workarounds that then stick around in boilerplates and tutorials for years.