The async support you linked, while useful, isn't really the same thing. It requires explicit, manual coordination between different parts of the code that want to fetch data. You're responsible yourself for batching fetches, polling, and running other code until the results are returned.

With Hack's async support, the runtime manages all of this for you. You call "await $query", and then your function is suspended until the data is available. Other code automatically runs until it too hits an await statement -- which might block it on MySQL, memcache, curl, or anything else, with no extra manual coordination needed. The runtime manages it all for you.

http://hhvm.com/blog/7091/async-cooperative-multitasking-for... has some examples for what this looks like with curl -- in the final example, notice how you can just "await" on a bunch of different things and let the runtime worry about coordinating all of them.