You are correct; by default, buttons do not get icons anymore. This is intentional.
We heard from many (UX) people that the first thing they always do, is to remove icons from buttons. We thought we would save you the work. We no longer want to put the 16x16 bitmap icons on buttons and we do not want to force standard glyphicons on everyone.
That being said, there is a cool new feature to quickly update icons throughout your project (Tools > Batch update button icons). So, you do not have to do it by hand!
See also this article on the new glyphicons.
I also think this isn't the best solutio. On the one hand you'll indeed have a lot of developers who don't want the icons on the buttons by default. For these people this solution may be productive and speed up development, but on the other hand a lot of other people still may want the icons on the butons by default.
So why don't solve this in a way best suited for both worlds? Like a setting which will allows you to simply include or exclude icons on buttons by default? This way, you preserve both workflows and people can work in a way that fits them most.