it's embedded all the way down
Good post. I think the key phrase is "from one operating system". One of the implicit promises of vertical software is that the SaaS vendor can be the technology partner that abstracts away a lot of the techno mumbo jumbo that business owners (especially SMBs) usually don't want to have to learn. We've seen over and over again that if you do a good job at solving a key businesses problem with software (e.g. scheduling / online booking) the buyer will listen when you have more functionality to offer them.