If you're curious about when it changed, here it is (though I believe most of this was rolled into HF18)...
Remove Posting Limit - Currently there is a 4-post per day soft limit on posts, after which author rewards are throttled. This limit will be removed, so that authors can create an unlimited number of posts without being penalized by the blockchain. (Bandwidth limits will still apply.) (GitHub Issue 732)
Ohh so it probably was before I even joined :)