Oh, I wonder if this means that Bittorrent Inc's own clients (e.g. uTorrent) are helping maintaining the DHT store by default now.
I'm guessing that your "by default now" may actually be in regards to BitComet and the v0.60 client that upset some folk?
Besides the BEP44 implementation magila mentioned, BitTorrent Inc. also assists with the DHT by operating a public bootstrap server at router.[bittorrent|utorrent].com, and provides the source too: https://github.com/bittorrent/bootstrap-dht
I mean DHT is "decntralized" once the client has a copy, but initially a client has to get a copy of it from somehwere.
And unless every client gets the DHT from a different source, the system seems "centralized" in that sense.
Thanks for the answer.