What's the big deal? Perhaps not, but the API would enable third party application development, taking Plurk to the larger population, allowing development of apps that show Plurk in a Twitter like style (perhaps a Mobile Style as well). And this is where the BIG DEAL comes in; this would allow Plurk to gain popularity, with users moving over to Plurk instead of the ever coughing and tumbling Twitter.
The API is not an official Plurk API and has been developed by Ryan Lim and has therefore been called RLPlurkAPI (God save me from re-typing this huge name!).
But that is not an issue of concern as long as the APIs let Plurk takes forward plunges to enhance the service, making it far more effective and user friendly.
Has Plurk earned its respect already? Well based on its similarity to Twitter (in terms of service) has attracted a lot of Twitter users and its different layout is pretty catchy; given the colors of the box and texts, the third party apps will bring about speedy changes as developers get a chance to bombard their ideas over and make Plurk an experience.
So what is the fuss about Plurk when we already have Jaiku, Pownce grappling at a similar service (forget Twitter for the time being). The reason is Plurk's blast ever since its launch, it had over 15,000 users within a week and the user base continually increasing. I personally think that the hype Plurk struck when the iron was hot and has tactfully capitalized on that.
On a personal note I would recommend that Plurk takes the APIs seriously and let the developers do what they do best. Make BIG out of the freedom they have.