Product Companies are quite distinct from Services Companies. Though in the cloud, it is quite hard to see the difference. It appears like all cloud companies do the same thing.
Lets try to understand the differences. A product vendor for e.g., a provider of subscription-based software applications sometimes sell services, but primarily to support its products. A services vendor relies on cloud consulting and implementation services as its primary stream, yet may see an opportunity for additional revenue with products.
Cloud based product vendors provide continuous product upgrades, support and maintenance as part of the subscription. Most of the product vendors revenues are recurring and result from the product-subscription model. Also, the cloud product vendor may use PaaS or IaaS for their base and depend on other cloud providers.
However, a service vendor works on the need of the companies, may be for very specific customizations or to build custom applications. Going with a service vendor would mean that the customer would have to bear the ongoing cost of activities such as customization, enhancement, maintenance and support.
For most cases, a product vendor is the best choice for companies when talking in terms of cost/value benefits of cloud computing. There is always continuous upgrades and support. In either case, it's important for a customer to understand what type of company it wants to do business with and choose accordingly, since there can be significant difference in costs.