I second this - developers need to remove them selves from their environment and become engrossed in what they are doing.
No headphones? That's would be business suicide, any decent developer will likely move very quickly.
What's the most important thing for devs? IMO being surrounded by like minded devs who enjoy their work. All the fluffy stuff around the office is not going to do anything to keep good devs, we can buy our own fluffy feel good stuff we don't *need* it from our employers (although it is welcome).
Hardware choices? That's not about keeping devs happy, it's a economic decision. Get them the best hardware you can afford if it makes their job quicker/easier/etc. There's nothing more to it..
We have our own toys already, I don't give a hoot what hardware I use at work as long as I'm not slowed down or restricted by it. If I am, then you've failed as an business since you're costing yourself hours of waiting for each dev each week, not a smart move.