First customer service will be automated or even non existant, and very poor. Secondly the product will have been 'tweaked' so many times for new markets and product extensions that it will be very fragile when you do something at the edges of its functionality (not what the other hundreds of millions are doing).
It shouldn't really be this way - it tells a lot about software engineering that a product run by a few enthused people alone can often (but by no means must) have better support and service than a product with huge resources.