FTFA : - "The issue is only really relevant in the case of very non-savvy or terminally lazy users, as it is trivially simple to install alternative browsers with or without the EU choice dialogue."
It might be trivially simple to Kelly Fiveash, and indeed to myself and no doubt most reading here, but it is far from trivially simple for a large proportion of users. They would be terrified of it.
Sounds like Kelly Fiveash is living in a bubble isolated from many PC users in the real world. Without the browser choice screen they are no more likely to change their new PC's browser than they are to replace the software in their new Volvo's engine control system.
A typical comment I get from friends (in the photography world, so a bit technical but not PC technical) when I suggest Firefox instead of IE :- "But won't that invalidate my guarantee?"
As for "only relevant", we are talking about 80% of PC users. Some "only".