Note that 11 percent of ten million is over a million users below 5.2.

So they are going to hassle a non-trivial number of users (in that not keeping up with WP updates is very hazardous to your site's health).

It's VERY easy to code around MySQL 4/ PHP 4.4 limits, in fact they are going to have to go out of their way to force WP3 not to support it.

But to be fair, a year of warning is plenty of notice.

I have a bigger problem with the drop of support for MySQL 4.1 because on small/medium sized MyISAM tables it is measurably faster than MySQL 5.x