But "open source"
means you have you know, the SOURCE? Nobody can take that away from you. A 'cloud hosted' API on the other hand - you own nothing, it's completely at the mercy of the hoster/developer.
Similar to me not really wanting to use Google for many things (contacts/calendar/mapping) - this is a partial reason for that - I CANNOT depend on a third party to be doing things in my best interest.
Give me the SOURCE of your API and I can implement it anywhere I fancy (see Mozilla Sync for instance, last I looked you COULD use their servers or host your own with open source software).
I'm not asking out of some sense of privilege, but what's the point of building a product or service that someone else can pull the plug on at any given time?