There are plenty of arguments either way between centralized trackers versus trackerless DHT. Centralized trackers are much simpler for everybody, they allow you to keep statistics on your torrents, and they let you control who can access a torrent. DHT is more robust, since it cannot be taken down except by extraordinary measures, and cheaper, since that's one less server you need to keep running. More importantly, in this case, it also lets you spread around the legal liability, diffusely enough that the network can't be taken down by lawsuits.
Let's be honest, that's the real reason TPB is doing this. For all their talk of this being the right technical decision, and not motivated by the current lawsuits, the fact is that they're potentially facing a lot of liability because they run a tracker in addition to indexing torrents. Switching to DHT exclusively means that they're free from that, and their defense that they're equivalent to a search engine has a better chance of working.
So here's the interesting point. If you want to shut down a website, it's relatively easy to do - there are several centralization points, such as the domain name, or the server it's hosted on, that are owned and paid for by people, and people are subject to the law. A fully decentralized service, on the other hand, is much more tricky. Take Freenet, for example. The system is specifically designed to be completely anonymous, secure, and deniable - if you're careful, it's next to impossible to prove that you downloaded or uploaded something from or to Freenet. I'll be blunt here - child pornography is traded occasionally on Freenet, and while there are a lot of people that would like to shut it down, for good reasons, it is basically impossible. If you want to shut down BitTorrent DHT, or the Freenet network, you're basically out of luck.
Here's the relevant question, then. How do you regulate a completely decentralized system? Is it even possible? I would argue that, with the Internet's current architecture, it's not. This is a huge deal - right now, it is possible to build completely secure and untraceable communication networks, at next to zero cost to yourself, which cannot be taken down by anything less than the scale of a massive military operation. It doesn't even have to have a lot of people using it. Take, as another example, any of the various mega-botnets running around these days. These are networks composed of millions of computers, next to impossible to shut down, where almost all of the participants in the network are there involuntarily.
What does it mean for society, now that communication has the potential to be completely unregulable? How do we shut down a terrorist cell, when they talk to each other over encrypted VoIP instead of cell networks? (Actually, that's not much of a problem. Despite what the government tells you, most terrorists would be lucky to set off a firecracker, much less talk about setting one off over VoIP.) Do laws about libel still mean anything, if speech can be truly, untraceably anonymous? What about copyright law? Now I'm drifting into old questions, though.
There are interesting parallels between legal regulation and hardware failure, actually. Decentralization, in its ability to protect against the latter, actually seems to prevent the former very effectively.