I was able to get a big external monitor but only after asking. It's not something that you're asked about when you start.
I don't work for a software or engineering company, and I enjoy the work, but I'd really like to be on a machine that really worked well for me and my needs. I really dislike Windows software in particular, and have found some real gems on OS X.
Too many companies try to nickle and dime IT spending. Saving a few hundred dollars or so on an employees machine isn't going to do you a lot of good if that means a lot of lost productivity.
The problem is that the people at the top often spend more time in meetings than working and only do email, PowerPoint, Word and Excel. They don't quite grasp how a better system could lead to more productivity, because their jobs aren't to produce things.
Of course, if you don't understand how your employees produce things, maybe you shouldn't be at the top.