Great example of why client side software is more exacting (and frightening) than building for the web. I wish I had more of these tales as ammo for future "native vs mobile web" debates.
What exactly protects web developers from this problem? Badly written AJAX-based code could do this just as easily as client software. Web development isn't a magic cure-all and it certainly doesn't protect you from the problem described in this post.
Part of the issue, a bit tangent to your point, is that when dealing with thick client software, once a version is released you can typically expect it to be in the field for quite some time. Many customers are upgrade-averse and simply won't upgrade a piece of software that is working suitably for them. Software developers have a bad habbit of fixing one bug and introducing another. With a web-based application you essentially control the release platform and can change things behind the scenes.
