(Disclaimer: I work for Protocol Labs on IPFS and other projects [not Filecoin though])

I'm not sure I understand what's different in the way "seeding" or "hosting" of data in Dat and Torrents compared to IPFS. All those requires you to initiate the transfer, nothing gets transferred by itself (unlike FreeNet for example).

Blocks in IPFS is just a detail that a file bigger than X MB gets split up into many smaller "files" so they can be reused between files and simpler to transfer. It has nothing to do with which peers are hosting the content.

In the end, in IPFS, Dat and Torrents, you download and share content based on a ID, and that ID can mean an entire archive of content, or just one picture.