A blockchain allows developers to out-source the running of a globally-available append-only log. Such a log is useful for building something like Trillian:
Ok but how does a globally-available append-only log help distribute applications ? The technology is probably interesting, but it doesn't help solve the problem at hand
If you can securely distribute the hash of the binary, you can probably also distribute a set of URLs representing where the binary can be downloaded from.
Bittorrent would fit well as a way of distributing the apps themselves, as that ecosystem already uses magnet links, and developers could quite cheaply run a node which acts as a seed of last resort.
Bittorrent has everything you'd need for distributing apps: of course the distribution of binaries is there, but it also has storing of arbitrary information, even mutable (http://bittorrent.org/beps/bep_0044.html). This way once you have a version you can fetch further versions by periodically polling the hash that contains the latest version.