Don't we need to define the term "cloud" before we even attempt answering this question? Cloud can be SaaS (according to Salesforce and many other SaaS companies). Cloud can be IaaS such as that provided by a datacenter owner/operator. Cloud can be shared elastic hosting such as that provided by Amazon, Azzure, etc.. Cloud can even be private elastic hosting or "Cloud in a box" such as that the client owns/controls/manages the physical hardware AND virtualization software. Cloud can be a hybrid solution such as what has already been mentioned... but effectively serves as any combination of the flavors listed above. Last but not least, Cloud can simply mean anything "online" for most who are not geeks and still think the internet works by way of magic.
Thus... if the term is not defined... for the sake of this thread... I don't see how anyone could argue that they are NOT already developing in the Cloud? So... iron.io, what does "cloud" mean to you?