Lets see... Your other browsers are STILL THERE, and if you open one of them, it will ask you if you want to make it your default browser.
Real freaking difficult.
On the other hand, it's not MSs responsibility to ensure that old versions of other peoples software is compliant with their new OS, so yes, it makes sense to have upgrades change the default to one they know will work. That way the users that prefer the other browsers can use the default one to download a new version of the one they prefer, even if their old version of it doesn't freaking work properly in the new OS.
There is nothing stopping you from easily changing the default, and there are reasons why an OS upgrade shouldn't leave the pre-upgrade default on an unverified 3rd party software. Don't like it, then welcome to the reality of having to cater to millions of virtual computer illiterates that will panic and freak if the slightest thing goes wrong. You are just a footnote of annoyance vs a possible flood of pissed off users.
I can complain about MS as much or more than virtually anyone that's sane, but look at the big picture rather than your own little reflection. If you want to complain, make it about something that is unreasonable, or just plain broken or F'd up. (There's lots of that out there. I'll give you one hint, don't do the express install, use the other one where you can pick what some of the defaults will be, you'll be shocked.)