Perhaps they don't own the rights to redistribute the Kindle version?
Anyhow, I would have preferred a simple text file. I don't see what PDF gives me except extra work to convert it to something else. Which is probably why, most likely, I'm not even going to read the thing.
You won't read their free book that you would have otherwise liked to have read because they don't distribute it in your preferred format but instead in 2 very ubiquitous formats that are easily converted? Really? This is not a personal attack but it is a criticism and I think it applies to a lot of people, really.
There seems to be this really weird trend where people seem to think they're entitled to free stuff when and how they want it. They don't quite come out and demand it but the subtext is clear as day. Your comment and much of the others exemplify this. You basically just said "I'm not reading it because it doesn't come in my preferred format" which isn't far from "they should release it in the format I desire". (it's not what you say but how you say it). Then there's that direct download link and the complaints about giving an email to get a PDF. That's entitlement. It seems the beggars believe they can also be choosers. Someone is giving something at no cost but people still feel they should be able to circumvent simply giving an email which they can unsubscribe from later quite easily. Imagine if 37Signals set up a booth on a public street corner and gave away hard copies of their book and then people went around saying "I shouldn't have to walk to the booth and say hi to Jason and DHH, they should just ship it to me". Its really not that big of a stretch!
I happen to notice a lot of this and it really gets to me.
The book itself seems interesting because of all the hype about it. But if I say I won't read it because it's not in the format I want it that suggests how important it really is to me, ie. not much.
I'm not saying I'm entitled to their book in my format, just that it would have been convenient.
There is only so much time available and even the "free" stuff costs, the more hoops they make you jump through.
If Coca Cola is giving away free six-packs at the local supermarket I probably won't drive half an hour to get there. But I also won't go to the neighborhood small market to get a single bottle because I'll realize I never wanted a Coca Cola to begin with, I was only curious what all the hype about the new flavor is all about.
(Maybe they want you to print it on really large paper and use it as your office wallpaper? That's a completely different strategy…)