The alternative would be to have phones turn off when they requested more power than was available. What do you think would cause people to want to replace their phones faster?
Case in point, when Apple explained the issue and their hack, people got way more interested in checking the state of their battery (wether they were affected or not), and there was a rush to replace used up batteries.
I tried to replace mine 2 months after the announcement, there was still a 3 weeks backlog of replacements.
Also to note: those phones were still turning off in some circumstances. It wasn't like Apple's hack completely removed the need to replace the faulty battery.
What part of this sentence did you not understand?
It's about WARNING the user before they do the upgrade so they 1) know what will happen and 2) know how they could fix it.