We realise we can't build it all. So the API enables Xero to stay flexible, if you really need additional features there will be suitable add-ons. We have Payroll in Australia.
No, only clients that want it. Accountants and bookkeepers can have clients on Xero as well as other platforms. There are incentives to have them all on Xero, but there are no requirements to be 100% Xero.
Accountants & Bookkeepers aren't charged, the model is to charge the end customer (business owner). The accountant or bookkeeper can choose to purchase Xero and then charge their client for it, or just absorb it into their existing pricing.
Through the Xero partner program there are some perks, including software to manage their practice.
http://www.xero.com/au/partners/
I'm keen to hear some more about your needs regarding the API limit. I've found most developers can work around the limit using batch calls. If there is a specific use case that is eating up a lot of API calls we can look at optimizing it.
The developer eco-system is very important. The lack of payroll didn't eventuate out of a fear of offending the developer community tho. Xero started in NZ without payroll. It was only after expanding to Australia that there was enough demand for payroll. At some stage payroll will be available in all regions.
I'm glad you have faith. Lots of features in the pipeline.
I handle developer relations at Xero. Happy to discuss your API limit needs when you've got the chance (email in profile). Secondly, it is our aim to have everything available via the API. We have been ramping up resources within the API team in order to keep pace with the rest of the product.